Prepare release 8.5.3

Workflow: Release stage 1 - create release PR (Cylc 8+ only), run: 55

Author: github-actions[bot]

CHANGES.md

@@ -11,6 +11,14 @@ $ towncrier create <PR-number>.<break|feat|fix>.md --content "Short description"
 
 <!-- towncrier release notes start -->
 
+## __cylc-8.5.3 (Released 2025-09-09)__
+
+### 🔧 Fixes
+
+[#6590](https://github.com/cylc/cylc-flow/pull/6590) - Fix validation of conditional expressions with negative integer offsets larger than `-P1`.
+
+[#6980](https://github.com/cylc/cylc-flow/pull/6980) - Fixed a bug where the GUI views would go blank when reloading a workflow.
+
 ## __cylc-8.5.2 (Released 2025-09-04)__
 
 ### 🚀 Enhancements

changes.d/6590.fix.md

@@ -53,7 +53,7 @@ def environ_init():
 
 environ_init()
 
-__version__ = '8.5.3.dev'
+__version__ = '8.5.3'
 
 
 def iter_entry_points(entry_point_name):