CLI tests fail with click 8.2

[ncoghlan]

Typer 0.16.0 resolved the known incompatibilities with click 8.2, so Typer's upper bound on click's version has been removed.

However, test_cli_invocation.py still suffers several failures when using click 8.2. On initial inspection, these appear to be related
to the test runner infrastructure, rather than to actual argument parsing failures, but it's hard to be certain about that, since the tests aren't running.

Accordingly, the temporary workaround is to conservatively add an upper bound on click to the main app requirements.

[ncoghlan]

Primary culprit here is this change in click to keep stdout and stderr separate when testing (output is the combined stream that reflects a merged console window): pallets/click#2522

Complicating factor in fixing the test cases is this remaining compatibility issue in typer: fastapi/typer#1240

Interim resolution:

• run the test cases with mix_stderr=False (so stdout and stderr are split regardless of click version)
• keep the upper bound on click's version until the implicit arg issue is fixed
• Edit: decided to adopt the workaround posted to the open PR and require click 8.2.0+ in CI