Bump dev version (cylc#6969)

Workflow: Release stage 2 - auto publish, run: 116

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]

cylc/flow/__init__.py

@@ -53,7 +53,7 @@ def environ_init():
 
 environ_init()
 
-__version__ = '8.5.2'
+__version__ = '8.5.3.dev'
 
 
 def iter_entry_points(entry_point_name):