.github/workflows/release-bazel: ask for secret

In addition to passing the secret down from release.yml,
release-bazel.yml has to ask for the secret explicitly.

Change-Id: I5621e11a157ed242dd19da01d5731b15b6291664
Reviewed-on: https://code-review.googlesource.com/c/re2/+/63970
Reviewed-by: Jeremy Kun <jkun@google.com>
Reviewed-by: Russ Cox <rsc@swtch.com>

.github/workflows/release-bazel.yml

@@ -12,6 +12,10 @@ on:
       tag_name:
         required: true
         type: string
+    secrets:
+      BCR_PUBLISH_TOKEN:
+        description: 'Token for pushing to re2-machine/bazel-central-registry'
+        required: true
 jobs:
   release:
     uses: bazel-contrib/publish-to-bcr/.github/workflows/publish.yaml@v0.2.2