ci: clang: Clone cached Zephyr repository

This commit updates the clang workflow to pre-clone the Zephyr
repository from the runner repository cache.

Note that the `origin` remote URL is reconfigured to that of the GitHub
Zephyr repository because the checkout action attempts to delete
everything and re-clone otherwise.

Signed-off-by: Stephanos Ioannidis <[email protected]>

Author: stephanosio

.github/workflows/clang.yaml

@@ -30,6 +30,13 @@ jobs:
         run: |
           # hotfix, until we have a better way to deal with existing data
           rm -rf zephyr zephyr-testing
+
+      - name: Clone cached Zephyr repository
+        continue-on-error: true
+        run: |
+          git clone /github/cache/zephyrproject/zephyr .
+          git remote set-url origin ${GITHUB_SERVER_URL}/${GITHUB_REPOSITORY}
+
       - name: Checkout
         uses: actions/checkout@v3
         with: