transport_local: fix cast warnings

home/kas/git/public/libgit2/src/transport_local.c: In function ‘cmp_refs’:
/home/kas/git/public/libgit2/src/transport_local.c:19:22: warning: cast discards ‘__attribute__((const))’ qualifier from pointer target type [-Wcast-qual]
/home/kas/git/public/libgit2/src/transport_local.c:20:22: warning: cast discards ‘__attribute__((const))’ qualifier from pointer target type [-Wcast-qual]

Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>

src/transport_local.c

@@ -16,8 +16,8 @@ typedef struct {
 
 static int cmp_refs(const void *a, const void *b)
 {
-	const char *stra = *(const char **) a;
-	const char *strb = *(const char **) b;
+	const char *stra = *(const char * const *) a;
+	const char *strb = *(const char * const *) b;
 
 	return strcmp(stra, strb);
 }