CI: Add clang++-12 regression tests run on Ubuntu (#936)

* ci: apply review comments on patch upload

* ci: add clang++-12 regression tests

---------

Co-authored-by: Johel Ernesto Guerrero Peña <[email protected]>

Author: jarzec

.github/workflows/regression-tests.yml

@@ -19,6 +19,8 @@ jobs:
         os: [ubuntu-latest]
         compiler: [g++-10, g++-13]
         include:
+          - os: ubuntu-20.04
+            compiler: clang++-12
           - os: macos-13
             compiler: clang++
           - os: windows-latest
@@ -28,7 +30,7 @@ jobs:
       uses: actions/checkout@v3
 
     - name: Run regression tests - Linux and macOS version
-      if: matrix.os == 'ubuntu-latest' || matrix.os == 'macos-13'
+      if: startsWith(matrix.os, 'ubuntu') || matrix.os == 'macos-13'
       run: |
         cd regression-tests
         bash run-tests.sh -c ${{ matrix.compiler }}