build: avoid duplicated CI runs

[caarlos0]

running on both push and pull_request end up running the same job twice for a push on a PR, which waste our CI minutes.

[codecov[bot]]

Codecov Report

Attention: 3823 lines in your changes are missing coverage. Please review.

Comparison is base (050a0d1) 50.52% compared to head (aeb33df) 47.77%. Report is 94 commits behind head on main.

:exclamation: Current head aeb33df differs from pull request most recent head 6264003. Consider uploading reports for the commit 6264003 to get more accurate results

Files	Patch %	Lines
pkg/web/git_lfs.go	25.15%	574 Missing and 27 partials :warning:
pkg/git/lfs.go	1.98%	297 Missing :warning:
pkg/ui/pages/repo/stash.go	0.00%	185 Missing :warning:
pkg/backend/webhooks.go	17.82%	162 Missing and 4 partials :warning:
pkg/ssh/cmd/webhooks.go	45.90%	156 Missing and 9 partials :warning:
pkg/ui/pages/repo/files.go	5.00%	152 Missing :warning:
pkg/lfs/http_client.go	5.92%	127 Missing :warning:
pkg/ui/pages/repo/refsitem.go	5.38%	123 Missing :warning:
pkg/backend/repo.go	40.59%	93 Missing and 27 partials :warning:
pkg/store/database/lfs.go	22.05%	105 Missing and 1 partial :warning:
... and 82 more

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #433 +/- ## ========================================== - Coverage 50.52% 47.77% -2.76% ========================================== Files 107 154 +47 Lines 8209 13068 +4859 ========================================== + Hits 4148 6243 +2095 - Misses 3767 6337 +2570 - Partials 294 488 +194 ```

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