test: add PostgrestError LocalizedError conformance test

- Add test to verify PostgrestError properly conforms to LocalizedError protocol
- Test ensures errorDescription property returns the expected error message
- Improves test coverage for error handling functionality

Author: grdsdev

Tests/HelpersTests/PostgrestErrorTests.swift

@@ -0,0 +1,19 @@
+//
+//  PostgrestErrorTests.swift
+//  Supabase
+//
+//  Created by Guilherme Souza on 07/05/24.
+//
+
+import Foundation
+import Helpers
+import XCTest
+
+final class PostgrestErrorTests: XCTestCase {
+
+    func testLocalizedErrorConformance() {
+        let error = PostgrestError(message: "test error message")
+        XCTAssertEqual(error.errorDescription, "test error message")
+    }
+
+}