[chore][exporterhelper] Fix feature gate setting for unit tests.

[sfc-gh-sili]

Description

Before fix: defer setFeatureGateForTest(t, usePullingBasedExporterQueueBatcher, enableQueueBatcher)
This means run setFeatureGateForTest in the end.

After fix: defer setFeatureGateForTest(t, usePullingBasedExporterQueueBatcher, enableQueueBatcher)()
This means: run setFeatureGateForTest immediately but execute the function returned from setFeatureGateForTest in the end.

Link to tracking issue

Fixes #

Testing

Documentation

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.62%. Comparing base (4d8c04f) to head (27d5d42).
Report is 16 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #11927      +/-   ##
==========================================
+ Coverage   91.59%   91.62%   +0.03%     
==========================================
  Files         449      447       -2     
  Lines       23761    23729      -32     
==========================================
- Hits        21763    21741      -22     
+ Misses       1623     1613      -10     
  Partials      375      375              

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