Check if RuboCop is available before searching for add-on #12332

Job	Run time
Ruby 3.1 on ubuntu-latest	14m 6s
Ruby 3.2 on ubuntu-latest	11m 57s
Ruby 3.3 on ubuntu-latest	12m 14s
Ruby 3.4 on ubuntu-latest	12m 9s
spelling	13s
Ruby 3.1 on macos-latest	9m 39s
Ruby 3.2 on macos-latest	8m 0s
Ruby 3.3 on macos-latest	7m 4s
Ruby 3.4 on macos-latest	7m 38s
Ruby 3.1 on windows-latest	22m 38s
Ruby 3.2 on windows-latest	22m 47s
Ruby 3.3 on windows-latest	23m 58s
Ruby 3.4 on windows-latest	23m 51s
build_node (ubuntu-latest)	1m 47s
build_node (macos-latest)	1m 58s
lint_node	33s
build_node (windows-latest)	5m 53s
lint_ruby	20s
Verify Jekyll website builds	7s
	3h 6m 52s

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