chore(deps): update dependency docker/buildx to v0.21.2 #9851

Job	Run time
ci / revisions	1s
ci / build / Build, stable, linux/amd64	1m 52s
ci / buildx / Build, stable, linux/arm64	2m 59s
ci / Anchore Container Scan	1m 17s
ci / Trivy Container Scan	1m 56s
ci / test-basic / Test container basic, stable	2m 44s
ci / Merge images, stable	15s
ci / test-localtime / Test container localtime, stable	2m 46s
ci / test-single-celery / Test container celery-single, stable	2m 45s
ci / test-novolume / Test container read-write, stable	2m 51s
ci / test-saml / Test container saml, stable	3m 6s
ci / test-split / Test container split, stable	2m 29s
ci / test-ssl / Test container basic, stable	2m 49s
ci / Tests, stable	1s
ci / Publish to Docker Hub, ${{ inputs.variant }}	0s
ci / Publish to GitHub, ${{ inputs.variant }}	0s
Create release on GitHub	0s
	27m 51s

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