CI: Update clang-format from 10 to 12

Microsoft Visual Studio 2019 ships with LLVM/Clang 12 as of Visual
Studio 2019 16.11.0 (August 10, 2021). LLVM/Clang 12 is available on all
platforms. This change should make it easier to have clang-format "just
work" on dev systems and be consistent across platforms without having
to use an outdated version.

.github/workflows/clang-format.yml

@@ -13,7 +13,7 @@ jobs:
 
       - name: Install clang format
         run: |
-          sudo apt-get install -y clang-format-10
+          sudo apt-get install -y clang-format-12
 
       - name: Check the Formatting
         run: |