📝 Add source examples for Python 3.9 and 3.10 (#715)

* 📝 Add source examples for Python 3.9 and 3.10

* ✅ Add tests for new source examples for Python 3.9 and 3.10, still needs pytest markers

* ✅ Add tests for fastapi examples

* ✅ Update tests for FastAPI app testing, for Python 3.9 and 3.10, fixing multi-app testing conflicts

* ✅ Require Python 3.9 and 3.10 for tests

* ✅ Update tests with missing markers

tests/conftest.py

@@ -1,5 +1,6 @@
 import shutil
 import subprocess
+import sys
 from pathlib import Path
 from typing import Any, Callable, Dict, List, Union
 
@@ -67,3 +68,9 @@ def get_testing_print_function(
         calls.append(data)
 
     return new_print
+
+
+needs_py39 = pytest.mark.skipif(sys.version_info < (3, 9), reason="requires python3.9+")
+needs_py310 = pytest.mark.skipif(
+    sys.version_info < (3, 10), reason="requires python3.10+"
+)