Update build image version to pr6541-9a9d7c46fb

Makefile

@@ -212,7 +212,7 @@ mimir-build-image/$(UPTODATE): mimir-build-image/*
 # All the boiler plate for building golang follows:
 SUDO := $(shell docker info >/dev/null 2>&1 || echo "sudo -E")
 BUILD_IN_CONTAINER ?= true
-LATEST_BUILD_IMAGE_TAG ?= pr7185-6a8507c909
+LATEST_BUILD_IMAGE_TAG ?= pr6541-9a9d7c46fb
 
 # TTY is parameterized to allow Google Cloud Builder to run builds,
 # as it currently disallows TTY devices. This value needs to be overridden