fix: only run the check labels workflow on PRs (#1336) #7961

Job	Run time
Typos Check	3s
Lints and doc tests on ubuntu-latest	6m 7s
Check PR labels	0s
Lints and doc tests on windows-latest	8m 7s
Unit tests on ubuntu-latest	10m 15s
Lints and doc tests on macos-13	8m 37s
Unit tests on windows-latest	15m 6s
Lints and doc tests on macos-14	3m 7s
Unit tests on macos-13	10m 2s
Unit tests on macos-14	8m 16s
Memory leak checks	2m 22s
CI status checks	1s
	1h 12m 3s

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