Fix concourse SBOM jobs

[supersven]

2>&1 | grep -v warning merged stderr into stdout, mixing nix warnings into the mapfile expression. Result: devShell/image name list polluted with non-name lines from stderr.

Drop the redirect so stdout carries only names and stderr stays separate.

This PR fixes the related jobs on CI and was tested there.

Ticket: https://wearezeta.atlassian.net/browse/WPB-26357

Checklist

• Add a new entry in an appropriate subdirectory of changelog.d
• Read and follow the PR guidelines

[Copilot]

Pull request overview

This PR fixes Concourse SBOM generation job scripts by preventing Nix warnings on stderr from being merged into stdout, which previously polluted the parsed devShell/image name lists (and could also drop lines via grep -v warning).

Changes:

• Remove 2>&1 | grep -v warning from nix eval calls that feed mapfile, keeping stdout strictly to the intended newline-separated names.
• Add an internal changelog entry describing the CI/SBOM job fix.

Reviewed changes

Copilot reviewed 1 out of 3 changed files in this pull request and generated 1 comment.

File	Description
hack/bin/create-nix-docker-image-sboms.sh	Stops merging/filtering stderr during image name discovery for SBOM generation.
hack/bin/create-nix-devshell-sbom.sh	Stops merging/filtering stderr during devShell name discovery for SBOM generation.
changelog.d/5-internal/fix-concourse-sbom-jobs	Documents the SBOM job/script fix in the internal changelog.

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[Copilot]

Pull request overview

Copilot reviewed 1 out of 3 changed files in this pull request and generated no new comments.