Add tests for `pullRequests.grouping` syntax

[rtyley]

A colleague mentioned to me that some of our pullRequests.grouping were not pulling in all the artifacts we were expecting - while looking into this, I realised that I wasn't 100% clear on where wildcards could be used in pullRequests.grouping, so I wrote this test to exercise all the cases that were relevant to us, and see what worked - this may be tested elsewhere to some extent in the Scala Steward codebase, but I think it's helpful to drill into the specific functionality with these new tests on PullRequestUpdateFilter.

See also

• https://github.com/scala-steward-org/scala-steward/issues/3655

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 89.83%. Comparing base (083ed69) to head (942528d). Report is 24 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3654   +/-   ##
=======================================
  Coverage   89.83%   89.83%           
=======================================
  Files         174      174           
  Lines        5045     5045           
  Branches      495      495           
=======================================
  Hits         4532     4532           
  Misses        513      513           

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