Bump steep from 1.4.0 to 1.5.0 in /steep #3181

Job	Run time
windows (windows-2019, ucrt)	1m 9s
windows (windows-2019, mswin)	1m 18s
windows (windows-2022, ucrt)	1m 19s
windows (windows-2022, mswin)	2m 5s
test (master-nightly-focal, test)	2m 41s
test (master-nightly-focal, stdlib_test)	2m 12s
test (master-nightly-focal, rubocop validate test_doc build test_generate_stdlib)	2m 20s
test (master-nightly-focal, lexer confirm_lexer)	4m 20s
test (master-nightly-focal, lexer compile)	4m 7s
test (3.2-dev-focal, test)	2m 50s
test (3.2-dev-focal, stdlib_test)	2m 9s
test (3.2-dev-focal, rubocop validate test_doc build test_generate_stdlib)	3m 17s
test (3.2-dev-focal, lexer confirm_lexer)	4m 52s
test (3.2-dev-focal, lexer compile)	3m 56s
test (3.1-dev-focal, test)	2m 40s
test (3.1-dev-focal, rubocop validate test_doc build test_generate_stdlib)	2m 26s
test (3.1-dev-focal, lexer confirm_lexer)	4m 10s
test (3.1-dev-focal, lexer compile)	4m 2s
test (3.0-dev-focal, test)	2m 37s
test (3.0-dev-focal, rubocop validate test_doc build test_generate_stdlib)	2m 58s
test (3.0-dev-focal, lexer confirm_lexer)	4m 37s
test (3.0-dev-focal, lexer compile)	4m 2s
	1h 6m 7s

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