C#: Make sure to run the .NET 10 sequentially.

Author: michaelnebel

csharp/ql/integration-tests/all-platforms/dotnet_10/test.py

@@ -1,5 +1,9 @@
+import pytest
+
+@pytest.mark.xdist_group("dotnet10")
 def test1(codeql, csharp):
     codeql.database.create()
 
+@pytest.mark.xdist_group("dotnet10")
 def test2(codeql, csharp):
     codeql.database.create(build_mode="none")