Remove usage of pytest.mark.capture from unified compiler tests

[mudit2812]

The pytest.mark.capture marker is for tests that should be run by the capture tests runner, but we want these tests to only run with the external-tests runner. Just to be safe, this PR is removing the capture marker and replacing it with explicit usage of the enable_disable_plxpr fixture, which is added under the hood automatically by the capture marker.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.40%. Comparing base (3a30488) to head (9bf47b4).
⚠️ Report is 11 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8234      +/-   ##
==========================================
- Coverage   99.41%   99.40%   -0.01%     
==========================================
  Files         548      548              
  Lines       56928    56928              
==========================================
- Hits        56593    56592       -1     
- Misses        335      336       +1     

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