Add classifier for Wagtail 4 (#116)

Co-authored-by: Dustin Ingram <[email protected]>

Author: gasman

Diff for: src/trove_classifiers/__init__.py

@@ -197,6 +197,7 @@
     "Framework :: Wagtail :: 1",
     "Framework :: Wagtail :: 2",
     "Framework :: Wagtail :: 3",
+    "Framework :: Wagtail :: 4",
     "Framework :: ZODB",
     "Framework :: Zope",
     "Framework :: Zope2",