extension: fix enterprise git commit hash display in tidb-server -V (#47647) (#47652)

close #47646

Author: ti-chi-bot

Makefile.common

@@ -67,7 +67,7 @@ LDFLAGS += -X "github.com/pingcap/tidb/util/versioninfo.TiDBGitBranch=$(shell gi
 LDFLAGS += -X "github.com/pingcap/tidb/util/versioninfo.TiDBEdition=$(TIDB_EDITION)"
 
 EXTENSION_FLAG =
-ifeq ($(shell if [ -d extension/enterprise/.git ]; then echo "true"; fi),true)
+ifeq ($(shell if [ -f extension/enterprise/.git ]; then echo "true"; fi),true)
 	EXTENSION_FLAG += -X "github.com/pingcap/tidb/util/versioninfo.TiDBEnterpriseExtensionGitHash=$(shell cd extension/enterprise && git rev-parse HEAD)"
 endif