build/bake: disable buildx metadata provenance

[crazy-max]

relates to https://github.com/tonistiigi/binfmt/actions/runs/27004688831/job/79696114031#step:12:2689

Error: An error occurred trying to start process '/home/runner/actions-runner/cached/2.334.0/externals/node24/bin/node' with working directory '/home/runner/work/binfmt/binfmt'. Argument list too long

This disables Buildx provenance data in the metadata output so large builds don't pass oversized metadata into the digest extraction step.

Buildx includes minimal provenance in metadata output by default, and large builds can make steps.bake.outputs.metadata large enough to hit process argument or environment limits when actions/github-script starts at

github-builder/.github/workflows/bake.yml

Lines 972 to 986 in 6cb8d00

	-
	name: Get image digest
	id: get-image-digest
	if: ${{ inputs.output == 'image' }}
	uses: actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3 # v9.0.0
	env:
	INPUT_TARGET: ${{ steps.prepare.outputs.target }}
	INPUT_METADATA: ${{ steps.bake.outputs.metadata }}
	with:
	script: |
	const inpTarget = core.getInput('target');
	const inpMetadata = JSON.parse(core.getInput('metadata'));
	const imageDigest = inpMetadata[inpTarget]['containerimage.digest'];
	core.info(imageDigest);
	core.setOutput('digest', imageDigest);