Use CreationTimestamp of volumebackup for gc check (#5518)

[ti-chi-bot]

This is an automated cherry-pick of #5518

What problem does this PR solve?

Closes #5517

What is changed and how does it work?

When GC expired volumebackup, we need to use creationtimestamp instead of commitTS, since commitTS is empty for failed backup.

Code changes

• Has Go code change
• Has CI related scripts change

Tests

• Unit test
• E2E test
• Manual test
• No code

Side effects

• Breaking backward compatibility
• Other side effects:

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation

Release Notes

Please refer to Release Notes Language Style Guide before writing the release note.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (227db87) 61.62% compared to head (9cac6e5) 61.65%.

Additional details and impacted files

@@               Coverage Diff               @@
##           release-1.5    #5523      +/-   ##
===============================================
+ Coverage        61.62%   61.65%   +0.02%     
===============================================
  Files              228      228              
  Lines            29152    29150       -2     
===============================================
+ Hits             17966    17973       +7     
+ Misses            9422     9417       -5     
+ Partials          1764     1760       -4     

Flag	Coverage Δ
unittest	61.65% <100.00%> (+0.02%)	⬆️

[ti-chi-bot]

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