Specifying stack parameters with `parameter-overrides` causes other parameters to revert to their default value

[sgdesmet]

The name parameter-overrides suggests similarity to aws cloudformation deploy --parameter-overrides while this actually functions similarly to aws cloudformation update --parameters, in that Cloudformation will use the default parameter value for stack parameters that were not specified, rather than using the previous value. The documentation for this github action isn't entirely clear on this either.

The updateStack(...) method in deploy.ts uses the AWS SDK v2 createChangeSet(...) call, of which the AWS SDK documentation has this to say:

Parameters — (Array)
A list of Parameter structures that specify input parameters for the change set. For more information, see the Parameter data type.

• ParameterKey — (String)
  The key associated with the parameter. If you don't specify a key and value for a particular parameter, CloudFormation uses the default value that's specified in your template.