build: make sure that dependabot is allowed to tag Docker images

[fengelniederhammer]

resolves #

Summary

Currently, dependabot PRs are failing on the "Tag images" step:

Run TAGS=(ghcr.io/genspectrum/lapis-silo:commit-2a21f6462fead47369031b1678f81564d7fdb3a5)
#1 [internal] pushing ghcr.io/genspectrum/lapis-silo:commit-2a21f6462fead47369031b1678f81564d7fdb3a5
#1 0.000 pushing sha256:adffed351a41aa07c46b0c47c0e1dede17cbfaa80fe5f4097143c57e3f3c7234 to ghcr.io/genspectrum/lapis-silo:commit-2a21f6462fead47369031b1678f81564d7fdb3a5
#1 ERROR: failed commit on ref "index-sha256:adffed351a41aa07c46b0c47c0e1dede17cbfaa80fe5f4097143c57e3f3c7234": unexpected status from PUT request to https://ghcr.io/v2/genspectrum/lapis-silo/manifests/commit-2a21f6462fead47369031b1678f81564d7fdb3a5: 403 Forbidden
------
 > [internal] pushing ghcr.io/genspectrum/lapis-silo:commit-2a21f6462fead47369031b1678f81564d7fdb3a5:
0.000 pushing sha256:adffed351a41aa07c46b0c47c0e1dede17cbfaa80fe5f4097143c57e3f3c7234 to ghcr.io/genspectrum/lapis-silo:commit-2a21f6462fead47369031b1678f81564d7fdb3a5
------
ERROR: failed commit on ref "index-sha256:adffed351a41aa07c46b0c47c0e1dede17cbfaa80fe5f4097143c57e3f3c7234": unexpected status from PUT request to https://ghcr.io/v2/genspectrum/lapis-silo/manifests/commit-2a21f6462fead47369031b1678f81564d7fdb3a5: 403 Forbidden
Error: Process completed with exit code 1.

PR Checklist

- [ ] All necessary documentation has been adapted or there is an issue to do so.
- [ ] The implemented feature is covered by an appropriate test.

[github-actions]

There is no change in the changelog. This PR will not produce a new releasable version.

[Taepper]

LGTM