show warning for unused block #675

Job	Run time
ruby-versions / Generate Ruby versions	8s
test (3.1, ubuntu-latest)	25s
test (3.1, macos-latest)	46s
test (3.1, windows-latest)	1m 36s
test (3.2, ubuntu-latest)	16s
test (3.2, macos-latest)	37s
test (3.2, windows-latest)	2m 30s
test (3.3, ubuntu-latest)	24s
test (3.3, macos-latest)	36s
test (3.3, windows-latest)	2m 15s
test (head, ubuntu-latest)	34s
test (head, macos-latest)	34s
test (head, windows-latest)	1m 10s
test (jruby, ubuntu-latest)	1m 47s
test (jruby, macos-latest)	2m 50s
test (jruby-head, ubuntu-latest)	1m 36s
test (jruby-head, macos-latest)	2m 53s
test (truffleruby, ubuntu-latest)	1m 38s
test (truffleruby, macos-latest)	1m 53s
test (truffleruby-head, ubuntu-latest)	2m 14s
test (truffleruby-head, macos-latest)	4m 33s
	31m 15s

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