Update release date for version 6.16.0

Author: thomashampson

docs/source/release/index.rst

@@ -13,7 +13,7 @@ Release Notes
 
 .. plot:: release/versions.py
 
-* v6.16.0 - 2026-06-22 - :doc:`release notes <v6.16.0/index>` - `github tag <https://github.com/mantidproject/mantid/releases/tag/v6.16.0>`__
+* v6.16.0 - 2026-06-25 - :doc:`release notes <v6.16.0/index>` - `github tag <https://github.com/mantidproject/mantid/releases/tag/v6.16.0>`__
 * v6.15.0 - 2026-02-23 - :doc:`release notes <v6.15.0/index>` - `github tag <https://github.com/mantidproject/mantid/releases/tag/v6.15.0>`__
 * v6.14.0 - 2025-10-23 - :doc:`release notes <v6.14.0/index>` - `github tag <https://github.com/mantidproject/mantid/releases/tag/v6.14.0>`__
 * v6.13.1 - 2025-07-24 - :doc:`release notes <v6.13.1/index>` - `github tag <https://github.com/mantidproject/mantid/releases/tag/v6.13.1>`__