Fix changelog typo (#26973)

Author: lunny

CHANGELOG.md

@@ -4,7 +4,7 @@ This changelog goes through all the changes that have been made in each release
 without substantial changes to our git log; to see the highlights of what has
 been added to each release, please refer to the [blog](https://blog.gitea.com).
 
-## [1.20.4](https://github.com/go-gitea/gitea/releases/tag/1.20.4) - 2023-09-08
+## [1.20.4](https://github.com/go-gitea/gitea/releases/tag/v1.20.4) - 2023-09-08
 
 * SECURITY
   * Check blocklist for emails when adding them to account (#26812) (#26831)