Enable errcheck linter and resolve found issues.

Signed-off-by: Xun Jiang <blackpiglet@gmail.com>

pkg/cmd/cli/bug/bug.go

@@ -162,7 +162,9 @@ func getKubectlVersion() (string, error) {
 	case <-time.After(kubectlTimeout):
 		// we don't care about the possible error returned from Kill() here,
 		// just return an empty string
-		kubectlCmd.Process.Kill()
+		if err := kubectlCmd.Process.Kill(); err != nil {
+			return "", fmt.Errorf("error killing kubectl process: %w", err)
+		}
 		return "", errors.New("timeout waiting for kubectl version")
 
 	case err := <-done: