chore(deps): update pre-commit hook executablebooks/mdformat to v0.7.21 #9592

Job	Run time
ci / revisions	3s
ci / build / Build, bleeding, linux/amd64	18s
ci / buildx / Build, bleeding, linux/arm64	30s
ci / Anchore Container Scan	1m 19s
ci / Trivy Container Scan	1m 50s
ci / test-basic / Test container basic, bleeding	3m 0s
ci / Merge images, bleeding	26s
ci / test-novolume / Test container read-write, bleeding	14m 17s
ci / test-saml / Test container saml, bleeding	9m 43s
ci / test-split / Test container split, bleeding	9m 12s
ci / test-localtime / Test container localtime, bleeding	14m 31s
ci / test-single-celery / Test container celery-single, bleeding	10m 29s
ci / test-ssl / Test container basic, bleeding	14m 33s
ci / Tests, bleeding	1s
ci / Publish to Docker Hub, ${{ inputs.variant }}	0s
ci / Publish to GitHub, ${{ inputs.variant }}	0s
	1h 20m 12s

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