fix(test-execute): prune fork-less items before evaluating filter_combinations

[spencer-tb]

Description

In execute mode, tests that are not valid for the session fork are still collected as fork-less items without their covariant params, and the forks plugin's filter_combinations predicates ran before these items were pruned, aborting the whole session with an INTERNALERROR (e.g. any full tree execute hive --fork=Osaka run).

Related Issues or PRs

Surfaced by running execute blobs hive mode runs of #2948.

Checklist

• Ran fast static checks to avoid CI fails, see Code Standards & Verifying Changes: just static
• PR title has the form <type>(<area>): <title>, where <type> and <area> come from an appropriate C-<type>, respectively A-<area>, label. The title should match the target squash commit message.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.41%. Comparing base (178d9f9) to head (87fa3fe).

Additional details and impacted files

@@               Coverage Diff                @@
##           forks/amsterdam    #3259   +/-   ##
================================================
  Coverage            93.41%   93.41%           
================================================
  Files                  625      625           
  Lines                37035    37035           
  Branches              3386     3386           
================================================
  Hits                 34597    34597           
  Misses                1668     1668           
  Partials               770      770           

Flag	Coverage Δ
unittests	93.41% <ø> (ø)

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[marioevz]

LGTM, thanks!