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

.github/workflows/test.yml

@@ -22,7 +22,7 @@ env:
 jobs:
   run-tests:
     name: Run tests
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@v4.1.7
       - uses: actions/setup-dotnet@v4.0.1