ci: pin pytest ubuntu version to 22..04 (#544)

Author: CyanVoxel

.github/workflows/pytest.yaml

@@ -5,7 +5,7 @@ on: [ push, pull_request ]
 jobs:
   pytest:
     name: Run tests
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
 
     steps:
       - name: Checkout repo