ci: run tests on ubuntu-22.04 instead of 24.04 for .NET Core 3.1

.github/workflows/test.yml

@@ -19,7 +19,7 @@ env:
 jobs:
   run-tests:
     name: Run tests
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
 
     steps:
       - uses: actions/checkout@v4.2.1