upgrade ubuntu

Author: maxbachmann

.github/workflows/linux-simple.yml

@@ -5,7 +5,7 @@ on: [push, pull_request]
 jobs:
   build:
     name: ${{matrix.cxx}}, C++${{matrix.std}}, ${{matrix.build_type}}
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     strategy:
       fail-fast: false
       matrix: