Fix changelog for Dockerfile with 2.7.3 cherry-pick

The apache#35026 has been cherry-picked to 2.7.3 (with updated changelog)
so we need to also update changelog in main.

docs/docker-stack/changelog.rst

@@ -58,10 +58,6 @@ here so that users affected can find the reason for the changes.
 Airflow 2.7
 ~~~~~~~~~~~
 
-* 2.7.4
-
-  * PIP caching for local builds has been enabled to speed up local custom image building
-
 * 2.7.3
 
   * Add experimental feature for select type of MySQL Client libraries during the build custom image via ``INSTALL_MYSQL_CLIENT_TYPE``
@@ -72,6 +68,8 @@ Airflow 2.7
 
   * Docker CLI version in the image is bumped to 24.0.6 version.
 
+  * PIP caching for local builds has been enabled to speed up local custom image building
+
 * 2.7.0
 
   * As of now, Python 3.7 is no longer supported by the Python community. Therefore, to use Airflow 2.7.0, you must ensure your Python version is