[Do Not Merge] ci: remove build artifacts

Signed-off-by: Akira Moroo <retrage01@gmail.com>

Author: retrage

.github/workflows/tests.yaml

@@ -14,6 +14,9 @@ jobs:
           - runner: bookworm-arm64
             coreboot-tests: false
     steps:
+      - name: Remove stale build artifacts
+        run: |
+          sudo rm -rf build || true
       - name: Code checkout
         uses: actions/checkout@v4
         continue-on-error: true