Ruby

Bump rbs from 3.7.0 to 3.8.0 in /steep #5915

Job	Run time
test (3.1, test)	2m 12s
test (3.2, test)	2m 10s
test (3.3, test)	2m 27s
test (3.4, test)	2m 38s
test (head, test)	2m 29s
test (head, stdlib_test rubocop)	2m 11s
test (3.4, stdlib_test)	2m 1s
test (3.4, test, --enable-frozen-string-literal)	2m 37s
test (3.4, stdlib_test, --enable-frozen-string-literal)	1m 59s
test (3.4, lexer templates compile confirm_lexer confirm_templates)	2m 59s
test (3.4, rubocop validate test_doc build test_generate_stdlib raap)	2m 39s
test (3.4, typecheck_test)	57s
	27m 19s

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