Bump dev version (#639)

Author: github-actions[bot]

cylc/uiserver/__init__.py

@@ -13,7 +13,7 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-__version__ = "1.5.1"
+__version__ = "1.5.2.dev"
 
 import os
 from typing import Dict