Move MuteFindings operation to private spec #18429

Job	Run time
test / test (jruby-9.4.12.0, ubuntu-latest)	3m 42s
test / test (3.2, ubuntu-latest)	3m 10s
examples / examples	3m 11s
pre-commit / pre-commit	1m 1s
test / test (2.7, ubuntu-latest)	3m 46s
report	7s
	14m 57s

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