Add CI step for drake_cmake_external dependencies

Use the new upgrade script in CI to verify that dependencies remain
synced over time.

Author: tyler-yankee

.github/workflows/ci.yml

@@ -58,3 +58,20 @@ jobs:
         run: |
           pip install ruamel.yaml
           python ./private/test/file_sync_test.py
+  check_cmake_deps:
+    name: sync drake_cmake_external deps
+    runs-on: ubuntu-latest
+    steps:
+      - name: checkout
+        uses: actions/checkout@v5
+      - name: setup
+        uses: actions/setup-python@v6
+      - name: upgrade test
+        run: |
+          output="$(python ./private/upgrade_cmake_externals.py 2>&1)"
+          printf "%s\n" "$output"
+          if [[ -n "$output" ]]; then
+            echo "Check Drake for possible upgrades to drake_cmake_external dependencies."
+            exit 1
+          fi
+        shell: bash