makefile: add non-file targets to .PHONY

Since we're not creating files named "help", "build" or "push" in those
targets, it's better to mark them as non-file targets. It will also allow make
to actually run a target even if there are files with those names present in
working directory.
1 job for topic/default/phony-targets in 21 seconds (queued for 1 second)