Add completion for global variables #11119

Job	Run time
build_node (ubuntu-latest)	1m 3s
Ruby 3.1 on ubuntu-latest	14m 4s
Ruby 3.2 on ubuntu-latest	15m 7s
Ruby 3.3 on ubuntu-latest	12m 33s
build_node (macos-latest)	1m 12s
lint_node	36s
Ruby 3.1 on macos-latest	9m 3s
lint_ruby	20s
build_node (windows-latest)	8m 6s
Ruby 3.2 on macos-latest	7m 45s
Ruby 3.3 on macos-latest	6m 44s
Ruby 3.1 on windows-latest	20m 26s
Verify Jekyll website builds	8s
Ruby 3.2 on windows-latest	19m 24s
Ruby 3.3 on windows-latest	21m 5s
	2h 17m 36s

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