Merge pull request #861 from smasato/chore/remove-ruby-debug-require #366

Job	Run time
lint	35s
test (3.3, 7.2, --enable-frozen-string-literal)	1m 49s
test (3.3, 7.1, --enable-frozen-string-literal)	1m 41s
test (3.3, 7.0, --enable-frozen-string-literal)	1m 35s
test (3.3, 6.1, --enable-frozen-string-literal)	1m 47s
test (3.2, 7.2)	1m 38s
test (3.2, 7.1)	1m 44s
test (3.2, 7.0)	1m 39s
test (3.2, 6.1)	1m 13s
test (3.1, 7.1)	1m 22s
test (3.1, 7.0)	1m 22s
test (3.1, 6.1)	1m 40s
test (3.0, 7.0)	1m 18s
test (3.0, 6.1)	1m 20s
test (jruby-9.4.8.0, 7.0)	4m 35s
test (2.7, 7.0)	1m 40s
test (2.7, 6.1)	1m 39s
test (2.7, 6.0)	1m 51s
test (jruby-9.3.15.0, 6.1)	4m 7s
test (2.6, 5.2)	1m 40s
	36m 15s

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