Ruby

Add type for `Enumerator::Chain` #6126

Job	Run time
test (3.1, test)	1m 3s
test (3.2, test)	1m 2s
test (3.3, test)	1m 19s
test (3.4, test)	1m 6s
test (head, test)	1m 2s
test (head, stdlib_test rubocop)	47s
test (3.4, stdlib_test)	48s
test (3.4, test, --enable-frozen-string-literal)	1m 6s
test (3.4, stdlib_test, --enable-frozen-string-literal)	51s
test (3.4, lexer templates compile confirm_lexer confirm_templates)	3m 22s
test (3.4, rubocop validate test_doc build test_generate_stdlib raap)	58s
test (3.4, typecheck_test)	57s
	14m 21s

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