Install matching clang-format version in CI

.github/workflows/ci.yml

@@ -18,14 +18,23 @@ jobs:
       - uses: actions/setup-python@v6
         with:
           python-version: '3.14'
+
       - name: Install PlatformIO Core
         run: pip install --upgrade platformio
 
+      - name: Install clang-format-21
+        run: |
+          wget https://apt.llvm.org/llvm.sh
+          chmod +x llvm.sh
+          sudo ./llvm.sh 21
+          sudo apt-get update
+          sudo apt-get install -y clang-format-21
+
       - name: Run cppcheck
         run: pio check --fail-on-defect medium --fail-on-defect high
 
       - name: Run clang-format
-        run: bin/clang-format-fix && git diff --exit-code
+        run: PATH="/usr/lib/llvm-21/bin:$PATH" ./bin/clang-format-fix && git diff --exit-code || (echo "Please run 'bin/clang-format-fix' to fix formatting issues" && exit 1)
 
       - name: Build CrossPoint
         run: pio run