put os into the matrix

Author: svlandeg

.github/workflows/test.yml

@@ -23,9 +23,9 @@ env:
 
 jobs:
   test:
-    runs-on: ubuntu-latest
     strategy:
       matrix:
+        os: [ ubuntu-latest ]
         python-version:
           - "3.8"
           - "3.9"
@@ -36,6 +36,7 @@ jobs:
           - pydantic-v1
           - pydantic-v2
       fail-fast: false
+    runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v4
       - name: Set up Python