Prevent Shadowenv from mutating BUNDLE_GEMFILE #11581

Job	Run time
build_node (ubuntu-latest)	1m 29s
build_node (macos-latest)	1m 44s
Ruby 3.1 on ubuntu-latest	16m 33s
lint_node	46s
build_node (windows-latest)	7m 9s
Ruby 3.2 on ubuntu-latest	14m 48s
Ruby 3.3 on ubuntu-latest	11m 39s
lint_ruby	24s
Ruby 3.1 on macos-latest	10m 53s
spelling	12s
Ruby 3.2 on macos-latest	8m 37s
Ruby 3.3 on macos-latest	7m 44s
Verify Jekyll website builds	9s
Ruby 3.1 on windows-latest	26m 58s
Ruby 3.2 on windows-latest	25m 32s
Ruby 3.3 on windows-latest	23m 2s
	2h 37m 39s

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