Ignore warnings from concurrent-ruby on JRuby 9.4. #66

Job	Run time
1.9.3 on ubuntu-20.04	31s
2.0 on ubuntu-20.04	34s
2.1 on ubuntu-20.04	34s
2.2 on ubuntu-20.04	49s
2.3 on ubuntu-20.04	39s
2.4 on ubuntu-20.04	34s
2.5 on ubuntu-20.04	38s
2.6 on ubuntu-20.04	40s
2.7 on ubuntu-20.04	51s
3.0 on ubuntu-20.04	32s
3.1 on ubuntu-20.04	27s
3.2 on ubuntu-20.04	38s
jruby-1.7 on ubuntu-20.04	3m 20s
jruby-9.0 on ubuntu-20.04	3m 25s
jruby-9.1 on ubuntu-20.04	2m 43s
jruby-9.2 on ubuntu-20.04	3m 32s
jruby-9.3 on ubuntu-20.04	3m 50s
jruby-9.4 on ubuntu-20.04	3m 59s
1.9.3 on windows-2019	2m 11s
2.0 on windows-2019	1m 12s
2.1 on windows-2019	1m 30s
2.2 on windows-2019	1m 52s
2.3 on windows-2019	2m 0s
2.4 on windows-2019	1m 42s
2.5 on windows-2019	2m 14s
2.6 on windows-2019	1m 53s
2.7 on windows-2019	1m 42s
3.0 on windows-2019	1m 32s
3.1 on windows-2019	1m 51s
3.2 on windows-2019	3m 0s
jruby-9.0 on windows-2019	3m 7s
jruby-9.1 on windows-2019	4m 3s
jruby-9.2 on windows-2019	5m 36s
jruby-9.3 on windows-2019	3m 57s
jruby-9.4 on windows-2019	4m 20s
2.0 on windows-2019 (x86)	1m 16s
head on ubuntu-20.04 (experimental)	32s
jruby-head on ubuntu-20.04 (experimental)	3m 23s
head on windows-2019 (experimental)	1m 38s
jruby-head on windows-2019 (experimental)	4m 14s
truffleruby-21 on ubuntu-20.04 (experimental)	1m 37s
	1h 24m 38s

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