build: skip pulling image

This step is only used for local development anyway.

Makefile

@@ -75,7 +75,6 @@ clean:
 	docker network prune
 
 prepare:
-	docker pull debian:bookworm-slim
 	FORCE_REBUILD=1 $(MAKE)
 
 .PHONY: all build tag push clean prepare release $(addprefix build_,$(JITSI_SERVICES))