chore: Add missing err assertion in test

Author: LashaJini

clients/pkg/promtail/targets/file/filetargetmanager_test.go

@@ -611,6 +611,7 @@ func TestFulfillKubePodSelector(t *testing.T) {
 	defer client.Stop()
 
 	ftm, err := newTestFileTargetManager(logger, client, ps, logDirName+"/*")
+	assert.NoError(t, err)
 
 	host := "test-host"