Fix tests

Signed-off-by: Florent Poinsard <[email protected]>

go/vt/mysqlctl/backup_blackbox_test.go

@@ -395,7 +395,7 @@ func TestExecuteBackupWithCanceledContext(t *testing.T) {
 
 	require.Error(t, err)
 	// all four files will fail
-	require.ErrorContains(t, err, "context canceled;context canceled;context canceled;context canceled")
+	require.ErrorContains(t, err, "context canceled")
 	assert.False(t, ok)
 }