Fix a leaking string buffer in `git show-ref --exclude-existing`. While
the buffer is technically not leaking because its variable is declared
as static, there is no inherent reason why it should be.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 builtin/show-ref.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/builtin/show-ref.c b/builtin/show-ref.c
index 56ee3250c5f..761669d28de 100644
--- a/builtin/show-ref.c
+++ b/builtin/show-ref.c
@@ -106,7 +106,7 @@ static int add_existing(const char *refname,
  */
 static int cmd_show_ref__exclude_existing(const char *match)
 {
-	static struct string_list existing_refs = STRING_LIST_INIT_DUP;
+	struct string_list existing_refs = STRING_LIST_INIT_DUP;
 	char buf[1024];
 	int matchlen = match ? strlen(match) : 0;
 
@@ -139,6 +139,8 @@ static int cmd_show_ref__exclude_existing(const char *match)
 			printf("%s\n", buf);
 		}
 	}
+
+	string_list_clear(&existing_refs, 0);
 	return 0;
 }
 
-- 
2.42.0