fix: resolve linting issues

- Check error return value from MarkFlagRequired using blank identifier
- Remove unused getEnvOrDefault function

Co-authored-by: Ona <no-reply@ona.com>

Author: leodido

cmd/sign-cache.go

@@ -49,7 +49,7 @@ func init() {
 	plumbingCmd.AddCommand(signCacheCmd)
 	signCacheCmd.Flags().String("from-manifest", "", "Path to newline-separated artifact paths file")
 	signCacheCmd.Flags().Bool("dry-run", false, "Log actions without signing or uploading")
-	signCacheCmd.MarkFlagRequired("from-manifest")
+	_ = signCacheCmd.MarkFlagRequired("from-manifest")
 }
 
 // runSignCache implements the main signing logic

pkg/leeway/signing/attestation.go

@@ -355,12 +355,4 @@ func validateSigstoreEnvironment() error {
 
 	log.Debug("Sigstore environment validation passed")
 	return nil
-}
-
-// getEnvOrDefault returns environment variable value or default
-func getEnvOrDefault(key, defaultValue string) string {
-	if value := os.Getenv(key); value != "" {
-		return value
-	}
-	return defaultValue
 }