Fast-follow: bump bazel.yml matrix image ref to bazel-ci:0.13.0 after it publishes

[balajinvda]

#343 adds a JDK (remotejdk_25) + Bazel pre-warm to ci/Dockerfile.bazel and bumps bazel-ci-image.yml to 0.13.0, but deliberately leaves the .github/workflows/bazel.yml matrix image: ref at 0.12.0. Reason: the 0.13.0 image only publishes to ghcr on merge to main, so bumping the consumer ref pre-merge would make every matrix row fail to pull the image (red PR).

Action after #343 merges and the 0.13.0 image publishes: bump the image: ref in .github/workflows/bazel.yml from 0.12.0 to 0.13.0 so the Java rows (and all rows) get the pre-warmed JDK/Bazel. Until then the Java rows work on 0.12.0 (bazelisk fetches the pinned Bazel and the hermetic JDK at runtime), just without the pre-warm speedup.

Relates to #343 and the caching work in #373.

[balajinvda]

Moot: the Java modules now use the image's packaged Temurin 25 via local_jdk (#343), so we stay on bazel-ci:0.12.0 - no 0.13.0 image and no consumer-ref bump. Closing.