Update flake8 requirement from <7.0.0,>=6.0.0 to >=6.0.0,<8.0.0 #22

Job	Run time
build (ubuntu-20.04, 3.9.9, minimal)	5m 9s
build (ubuntu-20.04, 3.9.9, maximal)	5m 22s
test-path-length	16s
build (ubuntu-20.04, 3.10.6, minimal)	5m 8s
build (ubuntu-20.04, 3.10.6, maximal)	5m 10s
test-api (maximal)	22s
lint-files (maximal)	15s
test-python (ubuntu-20.04, 3.9.9, minimal)	25s
test-python (ubuntu-20.04, 3.9.9, maximal)	18s
test-python (ubuntu-20.04, 3.10.6, minimal)	18s
test-python (ubuntu-20.04, 3.10.6, maximal)	21s
test-yaml (10, 0, minimal)	20s
test-yaml (10, 0, maximal)	14s
test-yaml (10, 1, minimal)	14s
test-yaml (10, 1, maximal)	21s
test-yaml (10, 2, minimal)	14s
test-yaml (10, 2, maximal)	17s
test-yaml (10, 3, minimal)	15s
test-yaml (10, 3, maximal)	15s
test-yaml (10, 4, minimal)	23s
test-yaml (10, 4, maximal)	15s
test-yaml (10, 5, minimal)	21s
test-yaml (10, 5, maximal)	14s
test-yaml (10, 6, minimal)	14s
test-yaml (10, 6, maximal)	21s
test-yaml (10, 7, minimal)	21s
test-yaml (10, 7, maximal)	21s
test-yaml (10, 8, minimal)	18s
test-yaml (10, 8, maximal)	24s
test-yaml (10, 9, minimal)	14s
test-yaml (10, 9, maximal)	17s
check-version-and-changelog	13s
check-for-functional-changes	0s
deploy	0s
	29m 10s

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