Fix remaining misuses of capturing the default file descriptors in flytectl unit tests

[eapolinario]

Tracking issue

Closes #5937

Why are the changes needed?

#5325 didn't fix all the misuses of the capturing of stdout+stderr in unit tests. This PR fixes the remaining cases.

What changes were proposed in this pull request?

We add the teardown as a defer statement to all uses of testutils.Setup.
Notice that in most cases we use barebones tests, which don't have a central place for setup/teardowns, so even though there's a comment explaining that Teardown has to be invoked, there's no automated way, at least to my knowledge, to do that.

edit: as suggested by @Sovietaced , we can leverage the setup call to hookup the call to cleanup (to restore stdout and stderr).

How was this patch tested?

Confirmed that tests ran successfully Ran unit tests in a loop a few times:

❯ for i in {1..100}; do
  go test -count=1 -cover ./... -race || break;
done

Setup process

Screenshots

Check all the applicable boxes

• I updated the documentation accordingly.
• All new and existing tests passed.
• All commits are signed-off.

Related PRs

Docs link

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 36.80%. Comparing base (f745030) to head (28c7a56).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5950      +/-   ##
==========================================
- Coverage   36.81%   36.80%   -0.01%     
==========================================
  Files        1310     1310              
  Lines      131032   131034       +2     
==========================================
- Hits        48234    48230       -4     
- Misses      78612    78618       +6     
  Partials     4186     4186              

Flag	Coverage Δ
unittests-datacatalog	51.58% <ø> (ø)
unittests-flyteadmin	54.02% <ø> (-0.03%)	⬇️
unittests-flytecopilot	11.73% <ø> (ø)
unittests-flytectl	62.39% <100.00%> (+<0.01%)	⬆️
unittests-flyteidl	6.92% <ø> (ø)
unittests-flyteplugins	53.64% <ø> (ø)
unittests-flytepropeller	42.90% <ø> (ø)
unittests-flytestdlib	55.39% <ø> (ø)

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[Sovietaced]

I'm not super familiar with this style of unit tests but I feel that passing *testing.T to the setup function and then using t.Cleanup(...) is less error prone because it doesn't rely on anyone remembering to use defer teardown().