Increase Pillow dependency range to include 9.x (#7831)

Fixes #7817

CHANGELOG.txt

@@ -42,6 +42,7 @@ Changelog
  * Fix: Ensure the `checkbox_aria_label` is used correctly in the Bulk Actions checkboxes (Vu Pham)
  * Fix: Prevent error on MySQL search backend when searching three or more terms (Aldán Creo)
  * Fix: Allow wagtail.search app migrations to complete on versions of SQLite without full-text search support (Matt Westcott)
+ * Fix: Update Pillow dependency to allow 9.x (Matt Westcott)
 
 
 2.15.1 (11.11.2021)

docs/releases/2.15.2.rst

@@ -19,6 +19,7 @@ Bug fixes
  * Ensure the ``checkbox_aria_label`` is used correctly in the Bulk Actions checkboxes (Vu Pham)
  * Prevent error on MySQL search backend when searching three or more terms (Aldán Creo)
  * Allow wagtail.search app migrations to complete on versions of SQLite without full-text search support (Matt Westcott)
+ * Update Pillow dependency to allow 9.x (Matt Westcott)
 
 
 Upgrade considerations

setup.py

@@ -27,7 +27,7 @@ install_requires = [
     "djangorestframework>=3.11.1,<4.0",
     "django-filter>=2.2,<22",
     "draftjs_exporter>=2.1.5,<3.0",
-    "Pillow>=4.0.0,<9.0.0",
+    "Pillow>=4.0.0,<10.0.0",
     "beautifulsoup4>=4.8,<4.10",
     "html5lib>=0.999,<2",
     "Willow>=1.4,<1.5",