bpo-39481: PEP 585 for difflib, filecmp, fileinput (#19422)

diff --git a/Lib/test/test_genericalias.py b/Lib/test/test_genericalias.py
index 196b059..4241eab 100644
--- a/Lib/test/test_genericalias.py
+++ b/Lib/test/test_genericalias.py
@@ -7,6 +7,9 @@
 )
 from collections.abc import *
 from contextlib import AbstractContextManager, AbstractAsyncContextManager
+from difflib import SequenceMatcher
+from filecmp import dircmp
+from fileinput import FileInput
 from mmap import mmap
 from ipaddress import IPv4Network, IPv4Interface, IPv6Network, IPv6Interface
 from itertools import chain
@@ -25,6 +28,9 @@
         for t in (type, tuple, list, dict, set, frozenset, enumerate,
                   mmap,
                   defaultdict, deque,
+                  SequenceMatcher,
+                  dircmp,
+                  FileInput,
                   OrderedDict, Counter, UserDict, UserList,
                   Pattern, Match,
                   AbstractContextManager, AbstractAsyncContextManager,