build: sync lockfiles and reuse in CI

.github/workflows/briefcase.yml

@@ -16,9 +16,7 @@ jobs:
       - uses: astral-sh/setup-uv@v3
       - name: Install dependencies
         run: |
-          uv pip compile src/runtime_requirements.txt --universal --generate-hashes --emit-index-url -o runtime.lock
-          git diff --exit-code runtime.lock
-          uv pip sync runtime.lock
+          uv pip sync --frozen runtime.lock
           uv tool install briefcase
       - name: Build with Briefcase
         run: briefcase build