[flytepropeller] Add tests in v1alpha

[DenChenn]

Tracking issue

Example: Related to #4209

Why are the changes needed?

Improve code tests coverage.

Check all the applicable boxes

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

Screenshots

Related PRs

#4234

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 36.85%. Comparing base (1652d4c) to head (49ccd36).
Report is 8 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5896      +/-   ##
==========================================
+ Coverage   34.96%   36.85%   +1.89%     
==========================================
  Files        1143     1309     +166     
  Lines      122098   130895    +8797     
==========================================
+ Hits        42688    48241    +5553     
- Misses      75721    78472    +2751     
- Partials     3689     4182     +493     

Flag	Coverage Δ
unittests-datacatalog	51.58% <ø> (ø)
unittests-flyteadmin	54.03% <ø> (+0.02%)	⬆️
unittests-flytecopilot	11.73% <ø> (ø)
unittests-flytectl	62.45% <ø> (?)
unittests-flyteidl	6.92% <ø> (ø)
unittests-flyteplugins	53.59% <ø> (ø)
unittests-flytepropeller	43.18% <ø> (+0.17%)	⬆️
unittests-flytestdlib	55.39% <ø> (ø)

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