Prepare release 1.4.3

Workflow: Release stage 1 - create release PR, run: 19

cylc/sphinx_ext/__init__.py

@@ -23,7 +23,7 @@
 from shutil import copyfile
 
 
-__version__ = '1.4.2'
+__version__ = '1.4.3'
 
 
 # map sub directory name to the name of the sphinx registration function