Fix PAC controller panic on empty commits in payload in gitlab

[zakisk]

fixed panic in PAC controller when commits are empty in event payload on tag push hook event when tag is created in gitlab.

https://issues.redhat.com/browse/SRVKP-6695

Changes

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[savitaashture]

@zakisk is it possible to add e2e

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 64.92%. Comparing base (316b3bc) to head (e0c863e). Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/provider/gitlab/parse_payload.go	0.00%	2 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1792 +/- ## ======================================= Coverage 64.92% 64.92% ======================================= Files 175 175 Lines 13396 13399 +3 ======================================= + Hits 8697 8699 +2 Misses 4116 4116 - Partials 583 584 +1 ```

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[zakisk]

@zakisk is it possible to add e2e

it is hard to reproduce this error, because it is intermittent. TestGitlabDeleteTagEvent was passing on my PR and on main as well but failed on nightly so we really don't know how to get that empty commits payload again on tag creation.

[chmouel]

it happens every time in nightly job even on restart

[chmouel]

but nonetheless fine to merge,