Update default bundle to 2.21.0 #4655

Job	Run time
Ruby analysis (macos-latest, linked)	1m 0s
Ruby analysis (ubuntu-latest, linked)	44s
Ruby analysis (macos-latest, default)	58s
Ruby analysis (ubuntu-latest, default)	43s
Ruby analysis (macos-latest, nightly-latest)	1m 10s
Ruby analysis (ubuntu-latest, nightly-latest)	42s
	5m 17s

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