Don't run `label-pr-size` once a PR has been merged #11469

Job	Run time
analyze-other (python)	1m 0s
analyze-other (actions)	56s
check-codeql-versions	49s
analyze-javascript (windows-2022, linked)	7m 20s
analyze-javascript (windows-2025)	6m 14s
analyze-javascript (ubuntu-24.04)	4m 36s
analyze-javascript (macos-15)	9m 33s
analyze-javascript (windows-2025, linked)	7m 1s
analyze-javascript (ubuntu-22.04)	4m 27s
analyze-javascript (windows-2022)	6m 8s
analyze-javascript (macos-14, linked)	9m 33s
analyze-javascript (macos-15, linked)	10m 40s
analyze-javascript (macos-14)	6m 33s
analyze-javascript (ubuntu-22.04, linked)	4m 28s
analyze-javascript (ubuntu-24.04, linked)	4m 43s
	1h 24m 1s

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