Merge pull request #129 from striezel-stash/fix-builds-on-old-compilers

Fix workflow failure for older compilers on Linux

Author: d-frey

.github/workflows/linux.yml

@@ -87,7 +87,7 @@ jobs:
           - clang++-9
         build_type: [Debug, Release]
 
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
 
     env:
       CXX: ${{ matrix.compiler }}