fix: extract image digest raw from yq

[steeve]

yq will quote the digest string, which will break image pushing.

For example:

INFO: Elapsed time: 1.673s, Critical Path: 1.12s
INFO: 5 processes: 1 internal, 4 darwin-sandbox.
INFO: Build completed successfully, 5 total actions
INFO: Running command line: bazel-bin/backend/api/cmd/push_push.sh
europe-west1-docker.pkg.dev/xx/xx
21:48:51 initCommand [WARN] JSON file output is now JSON by default (instead of yaml). Use '-oy' or '--output-format=yaml' for yaml output
Error: could not parse reference: xxxxxx@"sha256:ca70bd1e4c8fada66c93f31c58019ad72dc1f7a6d5a7fa900127e817c87ae679"

Remove the warning and unwrap the string.

[rahul-theorem]

Any context why this was reverted? We're hitting the same issue with oci_tarball failing due to the shasum being quoted

[thesayyn]

yq has made a breaking change and did not follow the semver rules while doing it. there was no way to support recent versions of yq in a backward-compatible way.

you should probably downgrade it as well. cross ref: bazel-contrib/bazel-lib#421