Check if RuboCop is available before searching for add-on #12331

Job	Run time
lint_ruby	20s
lint_node	27s
spelling	13s
Ruby 3.1 on ubuntu-latest	12m 29s
Ruby 3.2 on ubuntu-latest	12m 13s
build_node (ubuntu-latest)	1m 55s
Ruby 3.3 on ubuntu-latest	11m 7s
Verify Jekyll website builds	7s
build_node (macos-latest)	2m 12s
Ruby 3.4 on ubuntu-latest	11m 34s
build_node (windows-latest)	5m 49s
Ruby 3.1 on macos-latest	8m 28s
Ruby 3.2 on macos-latest	7m 32s
Ruby 3.3 on macos-latest	6m 46s
Ruby 3.4 on macos-latest	6m 32s
Ruby 3.1 on windows-latest	24m 49s
Ruby 3.2 on windows-latest	26m 40s
Ruby 3.3 on windows-latest	24m 44s
Ruby 3.4 on windows-latest	22m 39s
	3h 6m 36s

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