BUG: `vip_hci.objects.pppca` raises a `SyntaxError` in Python 3.9

[neutrinoceros]

vip_hci.objects.pppca uses the match/case statement, so it can't run on Python < 3.10
There's an actual warning about it from coverage in ci, but the fact it doesn't hard fails shows the module is probably not tested.

immediate options

• dropping 3.9: this is the "radical", but easy way to go. This version is very close to EOL by now so I could see this be uncontroversial. See https://devguide.python.org/versions/
• rewrite this module to replace match/case with something more portable, presumably if/elif/else. This is more work and I personally don't think it's worth it, but that's still an option.

follow up actionables:

• add tests for this module
• treat warnings into errors on CI so they cannot be silently ignored in the future (requires tinkering with all existing warnings)

[IainHammond]

I also don't mind dropping 3.9 as we'll need to do it soon anyway

[neutrinoceros]

Closed by #672