Use alternate quoting for older Python versions

Since Python 3.12, strings such as:

f"test_{object_name.replace(".", "_")}_class.py"

are allowed but older versions require single quotes around the dot and
underscore within the double quoted string.

Should quell CI error on Ubuntu Noble.

bindings/python/generate_tests.py

@@ -59,7 +59,7 @@ DO NOT EDIT this autogenerated file, run "make generate-pytests" instead
 """
 import Hamlib
 '''
-    filename = f"test_{object_name.replace(".", "_")}_class.py"
+    filename = f"test_{object_name.replace('.', '_')}_class.py"
     class_source = inspect.getsource(TestClass)
     expected_callables = repr(callables).replace(" ", "\n")
     expected_properties = repr(properties).replace(" ", "\n")