Fix blockquote color contrasts #3697

Job	Run time
lint (ubuntu-latest, 3.12)	21s
build-site (ubuntu-latest, 3.12)	1m 52s
run-pytest (ubuntu-latest, 3.9, rls)	2m 1s
build-site (macos-latest, 3.12)	2m 36s
run-pytest (ubuntu-latest, 3.10, rls)	2m 3s
build-site (windows-latest, 3.12)	6m 32s
run-pytest (ubuntu-latest, 3.11, rls)	1m 48s
build-site (ubuntu-latest, 3.9, old)	1m 40s
run-pytest (ubuntu-latest, 3.12, rls)	5m 16s
run-pytest (macos-latest, 3.12, rls)	3m 55s
run-pytest (windows-latest, 3.12, rls)	3m 53s
run-pytest (ubuntu-latest, 3.9, old)	1m 52s
run-pytest (ubuntu-latest, 3.12, dev)	4m 55s
audit (ubuntu-latest, 3.12)	4m 25s
profile (ubuntu-latest, 3.12)	1m 5s
	44m 14s

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