add test_clang_format workflow

Author: SizzinSeal

.github/workflows/test-clang-format.yml

@@ -0,0 +1,20 @@
+name: test-clang-format
+
+on:
+  push:
+    branches:
+      - '*'
+  pull_request:
+
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - uses: DoozyX/clang-format-lint-action@v0.18
+      with:
+        source: './src/fmtlib ./include/fmtlib'
+        extensions: 'hpp,cpp'
+        clangFormatVersion: 18