Fill in release date for 5.1.2

CHANGELOG.txt

@@ -69,7 +69,7 @@ Changelog
  * Maintenance: Simplify code for registering page listing action buttons (Matt Westcott)
 
 
-5.1.2 (xx.xx.20xx) - IN DEVELOPMENT
+5.1.2 (25.09.2023)
 ~~~~~~~~~~~~~~~~~~
 
  * Fix: Avoid use of `ignore_conflicts` when creating extra permissions for snippets, for SQL Server compatibility (Sage Abdullah)

docs/releases/5.1.2.md

@@ -1,6 +1,6 @@
-# Wagtail 5.1.2 release notes - IN DEVELOPMENT
+# Wagtail 5.1.2 release notes
 
-_Unreleased_
+_September 25, 2023_
 
 ```{contents}
 ---