Fix ci-config for go-version bumps (#18382)

The removal of the phony $(OUT) target was preventing `make ci-config`
from recognizing changes to .go-version, since it is not an explicit file target.
Reintroduce this change to get parity with ENT and fix go version bumps.

.circleci/Makefile

@@ -82,6 +82,7 @@ define GEN_CONFIG
 	@mv -f $@.tmp $@
 endef
 
+.PHONY: $(OUT)
 $(OUT): $(CONFIG_SOURCE) 
 	$(GEN_CONFIG)
 	@echo "$@ updated"