Move to clang-format-16 (#908)

Fixes #848

.github/actions/clang_format/action.yml

@@ -1,11 +1,23 @@
 name: Check format
-description: Check format using clang-format-11
+description: Check format using clang-format-16
 runs:
   using: composite
   steps:
-    # Github's ubuntu-20.04 image already has clang-format-11 installed
-    - run: |
-        find src unittests -type f \( -name '*.cpp' -o -name '*.h' -o -name '*.ipp' \) -print0 | xargs -0 clang-format-11 -i
+    - name: Add llvm repo
+      run: |
+        echo 'deb http://apt.llvm.org/focal/ llvm-toolchain-focal-16 main' | sudo tee -a /etc/apt/sources.list
+        wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | sudo apt-key add -
+      shell: bash
+
+    - name: Install packages
+      run: |
+        sudo apt update -qq
+        sudo apt install -y jq clang-format-16
+      shell: bash
+
+    - name: Run formatter
+      run: |
+        find src unittests -type f \( -name '*.cpp' -o -name '*.h' -o -name '*.ipp' \) -print0 | xargs -0 clang-format-16 -i
       shell: bash
 
     - name: Check for differences