Flip conditionals around package finders in pkg_resources (#3685)

- In Python 3.3+ importlib.machinery.FileFinder is always present,
  therefore we no longer need to keep the conditional
- In Python 3.12+ pkgutil.ImpImporter is removed, so we need a conditional
  to avoid using it directly.

changelog.d/3685.change.rst

@@ -0,0 +1 @@
+Fix improper usage of deprecated/removed ``pkgutil`` APIs in Python 3.12+.

pkg_resources/__init__.py

@@ -2187,10 +2187,10 @@ def resolve_egg_link(path):
     return next(dist_groups, ())
 
 
-register_finder(pkgutil.ImpImporter, find_on_path)
+if hasattr(pkgutil, 'ImpImporter'):
+    register_finder(pkgutil.ImpImporter, find_on_path)
 
-if hasattr(importlib_machinery, 'FileFinder'):
-    register_finder(importlib_machinery.FileFinder, find_on_path)
+register_finder(importlib_machinery.FileFinder, find_on_path)
 
 _declare_state('dict', _namespace_handlers={})
 _declare_state('dict', _namespace_packages={})
@@ -2344,11 +2344,11 @@ def file_ns_handler(importer, path_item, packageName, module):
         return subpath
 
 
-register_namespace_handler(pkgutil.ImpImporter, file_ns_handler)
-register_namespace_handler(zipimport.zipimporter, file_ns_handler)
+if hasattr(pkgutil, 'ImpImporter'):
+    register_namespace_handler(pkgutil.ImpImporter, file_ns_handler)
 
-if hasattr(importlib_machinery, 'FileFinder'):
-    register_namespace_handler(importlib_machinery.FileFinder, file_ns_handler)
+register_namespace_handler(zipimport.zipimporter, file_ns_handler)
+register_namespace_handler(importlib_machinery.FileFinder, file_ns_handler)
 
 
 def null_ns_handler(importer, path_item, packageName, module):