PR Metadata Validator: Remove "Needs Review" label for invalid PRs

[illicitonion]

If a PR is invalid, it's not ready for review, so we shouldn't mark it as such.

To go about this:

1. The relevant binary is pr-metadata-validator - its source is in https://github.com/CodeYourFuture/trainee-tracker/blob/main/src/bin/pr-metadata-validator.rs - you can build it with cargo build --bin pr-metadata-validator. Running it should tell you what args and env vars it needs. You can run it outside of the context of a GitHub Action.
2. There are three outcomes - successful validation, detected a known problem, unknown error. By the time we get to

   trainee-tracker/src/bin/pr-metadata-validator.rs

   Lines 81 to 88 in b0d8e12

   	let full_message = format!("{message}\n\nIf this PR is not coursework, please add the NotCoursework label (and message on Slack in #cyf-curriculum or it will probably not be noticed).");
   	eprintln!("{}", full_message);
   	octocrab
   	.issues(github_org_name, module_name)
   	.create_comment(pr_number, full_message)
   	.await
   	.expect("Failed to create comment with validation error");
   	exit(2);

   we have already exited for either successful validation or an unknown error.
3. We should be able to use octocrab's existing remove_label function
4. We probably want to modify the comment we post to say this has been done, and the user should re-add the label once it's been fixed.

https://github.com/CodeYourFuture/actions/blob/main/validate-pr-metadata/action.yml defines the GitHub Action YAML in case it's needed for reference, but I don't imagine we'll need to change it.

[LonMcGregor]

@illicitonion Do you have advice for how to set up a testing environment (rather than needing to request an access token for the live repositories)?

I've tried to run this on a PR in a personal repository and it refuses to run, stating it cant find a sprint label.

[illicitonion]

Personally for local testing I tend to just use a personal access token with the permissions it'll need, and iterate on a real (draft) PR I open against our actual repos.

Sprint label finding - in general the "matching against an issue" logic is to find all of the assignments (

trainee-tracker/src/course.rs

Lines 152 to 249 in f8c15f2

	for label in labels {
	if let Some(sprint_number) = label.name.strip_prefix("📅 Sprint ") {
	if sprint.is_some() {
	return Err(Error::UserFacing(format!(
	"Failed to parse issue {} - duplicate sprint labels",
	html_url
	)));
	}
	match NonZeroUsize::from_str(sprint_number) {
	Ok(sprint_number) => {
	sprint = Some(sprint_number);
	}
	Err(_err) => {
	return Err(Error::UserFacing(format!(
	"Failed to parse issue {} - sprint label wasn't (non-zero) number: {}",
	html_url, label.name
	)))
	}
	}
	}
	if let Some(label) = label.name.strip_prefix("Submit:") {
	if submit_label.is_some() {
	return Err(Error::UserFacing(format!(
	"Failed to parse issue {} - duplicate submit labels",
	html_url
	)));
	}
	submit_label = Some(label);
	}
	if label.name == "🏕 Priority Mandatory" {
	if optionality.is_some() {
	return Err(Error::UserFacing(format!(
	"Failed to parse issue {} - duplicate priority labels",
	html_url
	)));
	}
	optionality = Some(AssignmentOptionality::Mandatory)
	} else if label.name == "🏝️ Priority Stretch" {
	if optionality.is_some() {
	return Err(Error::UserFacing(format!(
	"Failed to parse issue {} - duplicate priority labels",
	html_url
	)));
	}
	optionality = Some(AssignmentOptionality::Stretch)
	}
	}
	let sprint = sprint.ok_or_else(|| {
	Error::UserFacing(format!(
	"Failed to parse issue {} - no sprint label.{}",
	html_url, BAD_LABEL_SUFFIX,
	))
	})?;
	let submit_label = match submit_label {
	Some(submit_label) => submit_label,
	// TODO: For now we treat a missing Submit label as an issue to ignore.
	// When all issues have Submit labels, we should error if they're missing.
	None => {
	return Ok(Some((sprint, None)));
	}
	};
	let optionality = optionality.ok_or_else(|| {
	Error::UserFacing(format!(
	"Failed to parse issue {} - no priority label.{}",
	html_url, BAD_LABEL_SUFFIX
	))
	})?;
	let assignment = match submit_label {
	"None" => None,
	"PR" => Some(Assignment::ExpectedPullRequest {
	title: title.clone(),
	html_url: html_url.clone(),
	optionality,
	}),
	"Codility" => {
	// TODO: Handle these.
	None
	}
	"Issue" => {
	// TODO: Handle these.
	None
	}
	"Slack" => {
	// TODO: Handle these.
	None
	}
	other => {
	return Err(Error::UserFacing(format!(
	"Failed to parse issue {} - submit label wasn't recognised: {}",
	html_url, other
	)));
	}
	};

). Basically looks through each Issue in the repo, and looks at their label. It expects:

• Exactly one label to have prefix 📅 Sprint and then a number
• At most one label which starts Submit: - for PRs it expects this to be Submit:PR, it ignores all other submit-types.
• Exactly one label which is either 🏕 Priority Mandatory or 🏝️ Priority Stretch.
• It ignores all other labels.