typing_extensions bug

For weekend/evenings:

For the bug, `vcspull/types.py` line 36 raises 

```
from typing_extensions improt NotRequired, TypedDict
```

CI should catch this by doing a test run with only real deps

Do something like libtmux:

https://github.com/tmux-python/libtmux/blob/dd1904e6624d26600357e668f7a8777d8753fdd3/.github/workflows/tests.yml#L26-L33