Use a custom bazel-postsubmit.yml file for Bazel in downstream pipeline (#1878)

Fixes https://github.com/bazelbuild/bazel/issues/21292

After
https://github.com/bazelbuild/bazel/commit/a54a393d209ab9c8cf5e80b2a0ef092196c17df3,
the canonical repo name returned by Bazel@HEAD no longer matches the
name in MODULE.bazel.lock, therefore we need to run `bazel mod deps
--lockfile_mode=update` to re-generate the lockfile before running the
build.

This is done by changing the postsubmi.yml file for Bazel to a custom
version located in the CI repo, which can be updated by running
`./update-bazel-postsubmit.sh` under `./pipelines`.

We may revert this change after we update Bazel to 7.1 for building
Bazel itself.
4 files changed