Update changelog for 1.5.4 release

Author: jluethi

CHANGELOG.md

@@ -1,10 +1,10 @@
 **Note**: Numbers like (\#123) point to closed Pull Requests on the fractal-tasks-core repository.
 
 # Unreleased
-* Tasks:
-    * Catch `FileNotFoundError` in `apply_registration_to_image` task when race conditions with the reference cycle are hit (\#971).
 
 # 1.5.4
+* Tasks:
+    * Catch `FileNotFoundError` in `apply_registration_to_image` task when race conditions with the reference cycle are hit (\#971).
 * Dependencies:
     * Pin `lxml` to `<=5.4.0` (\#963).