Adjust regular expression for base64_encoded? to avoid 'character cla… #627

Job	Run time
rubocop	33s
Unit test (ubuntu-22.04, 3.1)	3m 41s
Unit test (ubuntu-22.04, 3.4)	3m 45s
Unit test (ubuntu-22.04, jruby-9.4)	2m 40s
Unit test (ubuntu-22.04, jruby-10.0)	2m 47s
Unit test (ubuntu-22.04, 3)	3m 48s
Unit test (ubuntu-22.04, 3.2)	3m 36s
Unit test (macos-latest, 3.4)	2m 18s
Unit test (ubuntu-22.04, truffleruby)	5m 35s
Unit test (macos-latest, 3.3)	2m 33s
Unit test (macos-latest, 3)	2m 50s
Unit test (ubuntu-22.04, 3.3)	3m 43s
Unit test (macos-latest, 3.1)	1m 45s
Unit test (macos-latest, 3.2)	1m 50s
Unit test (windows-latest, 3.3)	3m 27s
Unit test (macos-latest, jruby-10.0)	3m 37s
Unit test (macos-latest, truffleruby)	4m 22s
Unit test (macos-latest, jruby-9.4)	3m 15s
Unit test (windows-latest, 3.2)	3m 23s
Unit test (windows-latest, 3.4)	3m 33s
Unit test (windows-latest, 3.1)	3m 17s
Unit test (windows-latest, 3)	3m 24s
finish	4s
	1h 9m 46s

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