Add 5.1.2 backport changelog entry for #10857

CHANGELOG.txt

@@ -63,6 +63,7 @@ Changelog
  * Fix: Change spreadsheet export headings to match listing view column headings (Christer Jensen, Sage Abdullah)
  * Fix: Fix numbers, booleans, and `None` from being exported as strings (Christer Jensen)
  * Fix: Restore fallback on full-word search for snippet choosers and generic index views (Matt Westcott)
+ * Maintenance: For Python 3.13 support - upgrade Willow to v1.6.2, replace `imghdr` with Willow's built-in MIME type detection (Jake Howard)
 
 
 5.1.1 (14.08.2023)