utils/gems: don't run `bundle clean`. #27664

Job	Run time
syntax	1m 30s
tap syntax	7m 47s
formula audit	6m 1s
cask audit	3m 0s
vendored gems	38s
docker	4m 42s
test default formula (Ubuntu 22.04)	4m 22s
update-test (Ubuntu 22.04)	57s
tests (online)	9m 3s
test default formula (Ubuntu 20.04)	5m 52s
update-test (macOS 13)	52s
tests (generic OS)	5m 59s
test default formula (macOS 13 x86_64)	2m 28s
tests (Ubuntu 22.04)	5m 48s
test default formula (macOS 14 arm64)	1m 16s
tests (Ubuntu 20.04)	6m 44s
tests (macOS 13 x86_64)	6m 24s
tests (macOS 14 arm64)	5m 0s
	1h 18m 23s

Provide feedback