[gh-actions](deps): Bump docker/build-push-action from 6.4.0 to 6.9.0 #547

Job	Run time
build (./images/gh-gl-sync, ghcr.io/spack/ci-bridge:0.0.42)	1m 20s
build (./images/ci-key-clear, ghcr.io/spack/ci-key-clear:0.0.2)	1m 8s
build (./images/gitlab-stuckpods, ghcr.io/spack/stuckpods:0.0.1)	2m 43s
build (./images/gitlab-clear-pipelines, ghcr.io/spack/gitlab-clear-pipelines:0.0.1)	49s
build (./images/gitlab-delete-stale-branches, ghcr.io/spack/gitlab-delete-stale-branches:0.0.1)	1m 3s
build (./images/gitlab-skipped-pipelines, ghcr.io/spack/gitlab-skipped-pipelines:0.0.2)	51s
build (./images/notary, ghcr.io/spack/notary:latest)	2m 1s
build (./images/python-aws-bash, ghcr.io/spack/python-aws-bash:0.0.2)	1m 31s
build (./images/snapshot-release-tags, ghcr.io/spack/snapshot-release-tags:0.0.4)	1m 10s
build (./images/cache-indexer, ghcr.io/spack/cache-indexer:0.0.3)	1m 25s
build (./analytics, ghcr.io/spack/django:0.3.16)	4m 32s
build (./images/ci-prune-buildcache, ghcr.io/spack/ci-prune-buildcache:0.0.4)	15m 7s
build (./images/protected-publish, ghcr.io/spack/protected-publish:0.0.1)	2m 2s
	35m 42s

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