ref_transaction_commit(): delete extra "the" from error message

While we are in the area, let's remove a superfluous definite article
from the error message that is emitted when the reference cannot be
locked. This improves how it reads and makes it a bit shorter.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>

refs.c

@@ -3844,7 +3844,7 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 				? TRANSACTION_NAME_CONFLICT
 				: TRANSACTION_GENERIC_ERROR;
 			reason = strbuf_detach(err, NULL);
-			strbuf_addf(err, "Cannot lock the ref '%s': %s",
+			strbuf_addf(err, "Cannot lock ref '%s': %s",
 				    update->refname, reason);
 			free(reason);
 			goto cleanup;