workflows: update actions/github-script to v9 (#4305)

GitHub Actions deprecated Node.js 20 and warns when running
actions/github-script@v7 in the setup-bazel composite action. Bump
actions/github-script to v9 (which targets Node.js 24) and add the
composite action directory to Dependabot so future action updates are
tracked automatically.

.github/actions/setup-bazel/action.yaml

diff --git a/.github/actions/setup-bazel/action.yaml b/.github/actions/setup-bazel/action.yaml
index 6e7e49e..aac5fd6 100644
--- a/.github/actions/setup-bazel/action.yaml
+++ b/.github/actions/setup-bazel/action.yaml
@@ -51,7 +51,7 @@
     # process tables and child environments.
     - name: Write secret to user.bazelrc
       if: ${{ inputs.buildbuddy_api_key != '' }}
-      uses: actions/github-script@v7
+      uses: actions/github-script@v9
       with:
         script: |
           const fs = require('fs');

.github/dependabot.yml

diff --git a/.github/dependabot.yml b/.github/dependabot.yml
index 5733fc1..8aa2155 100644
--- a/.github/dependabot.yml
+++ b/.github/dependabot.yml
@@ -3,7 +3,9 @@
 updates:
   # Maintain dependencies for GitHub Actions
   - package-ecosystem: "github-actions"
-    directory: "/"
+    directories:
+      - "/"
+      - "/.github/actions/setup-bazel"
     schedule:
       interval: "weekly"