Update builder image to ubuntu-22.04

GitHub has deprecated and removed the ubuntu-20.04 builder image.
This commit updates the build process to use the ubuntu-22.04
image instead.

Author: wnienhaus

.github/workflows/run_tests.yaml

@@ -11,7 +11,7 @@ on: [push, pull_request]
 
 jobs:
   tests:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     steps:
     - uses: actions/checkout@v3
       with: