Mark all targets as phony

Ref: https://www.gnu.org/software/make/manual/html_node/Phony-Targets.html

Makefile

@@ -1,4 +1,4 @@
-.PHONY: clean-pyc develop lint test coverage
+.PHONY: clean-pyc develop lint-server lint-client lint-docs lint format-server format-client format test coverage
 
 help:
 	@echo "clean-pyc - remove Python file artifacts"