fix: fix a lint problem

pkg/engine/runtime/terraform/util.go

@@ -26,11 +26,6 @@ type InstallOption struct {
 	Intent     *apiv1.Intent
 }
 
-type installResult struct {
-	execPath string
-	err      error
-}
-
 // check and install the terraform executable binary if it has not been downloaded.
 func (io *InstallOption) CheckAndInstall() error {
 	if len(io.Intent.Resources) < 1 {
@@ -159,7 +154,7 @@ func getTerraformInstallDir() (string, error) {
 	installDir := filepath.Join(kusionDir, tfInstallSubDir)
 
 	if _, err = os.Stat(installDir); os.IsNotExist(err) {
-		if err := os.Mkdir(installDir, 0755); err != nil {
+		if err := os.Mkdir(installDir, 0o755); err != nil {
 			return "", fmt.Errorf("failed to create terraform install directory: %v", err)
 		}
 	}