Hide default gems warnings for Ruby 3.4. #27609

Job	Run time
syntax	1m 24s
formula audit	6m 8s
cask audit	2m 30s
tap syntax	8m 13s
tests (online)	8m 47s
docker	4m 26s
tests (generic OS)	5m 52s
update-test (Ubuntu 22.04)	1m 7s
tests (Ubuntu 22.04)	6m 19s
update-test (macOS 13)	53s
vendored gems	49s
tests (Ubuntu 20.04)	7m 17s
tests (macOS 13 x86_64)	7m 24s
test default formula (Ubuntu 22.04)	4m 20s
tests (macOS 14 arm64)	4m 13s
test default formula (Ubuntu 20.04)	5m 30s
test default formula (macOS 13 x86_64)	2m 27s
test default formula (macOS 14 arm64)	1m 13s
	1h 18m 52s

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