Make find_nothing return an (empty) Generator of Distribution

This aligns with `find_eggs_in_zip` and `find_on_path` and ensures `find_distributions` always returns a generator

newsfragments/4249.bugfix.rst

@@ -0,0 +1 @@
+Ensure `pkg_resources.find_distributions` always returns a `Generator` as per its docstring by making `pkg_resources.find_nothing` yield nothing rather than returning an empty `tuple` -- by :user:`Avasam`

pkg_resources/__init__.py

@@ -27,7 +27,7 @@
 import time
 import re
 import types
-from typing import Protocol
+from typing import Generator, Protocol
 import zipfile
 import zipimport
 import warnings
@@ -2089,8 +2089,11 @@ def find_eggs_in_zip(importer, path_item, only=False):
 register_finder(zipimport.zipimporter, find_eggs_in_zip)
 
 
-def find_nothing(importer, path_item, only=False):
-    return ()
+def find_nothing(
+    importer, path_item, only=False
+) -> Generator["Distribution", None, None]:
+    return
+    yield
 
 
 register_finder(object, find_nothing)