build.make: properly declare push-multiarch

pohly · pohly · commit 5231f05d8b2f · 2020-06-03T11:04:29.000+02:00
It's not a real file and thus should better be marked as phony.
diff --git a/build.make b/build.make
@@ -166,6 +166,7 @@ check-pull-base-ref:
 		exit 1; \
 	fi
 
+.PHONY: push-multiarch
 push-multiarch: $(CMDS:%=push-multiarch-%)
 
 clean:
