build: upgrades lint package

Author: CodingAleCR

pubspec.yaml

@@ -16,5 +16,5 @@ dependencies:
   validators: ^3.0.0
 
 dev_dependencies:
-  lints: ^4.0.0
+  lints: ^6.1.0
   test: ^1.25.8

test/extensions/base_reponse_test.dart

@@ -1,7 +1,7 @@
 import 'package:http_interceptor/http_interceptor.dart';
 import 'package:test/test.dart';
 
-main() {
+void main() {
   group('BaseResponse.copyWith: ', () {
     test('Response is copied from BaseResponse', () {
       // Arrange

test/extensions/base_request_test.dart

@@ -3,7 +3,7 @@ import 'dart:convert';
 import 'package:http_interceptor/http_interceptor.dart';
 import 'package:test/test.dart';
 
-main() {
+void main() {
   group('BaseRequest.copyWith: ', () {
     test('Request is copied from BaseRequest', () {
       // Arrange

test/extensions/request_test.dart

@@ -4,7 +4,7 @@ import 'dart:io';
 import 'package:http_interceptor/http_interceptor.dart';
 import 'package:test/test.dart';
 
-main() {
+void main() {
   late BaseRequest baseRequest;
   late Request request;
 

test/extensions/response_test.dart

@@ -1,7 +1,7 @@
 import 'package:http_interceptor/http_interceptor.dart';
 import 'package:test/test.dart';
 
-main() {
+void main() {
   late BaseResponse baseResponse;
   late Response response;
 

test/http/http_methods_test.dart

@@ -1,7 +1,7 @@
 import 'package:http_interceptor/http/http_methods.dart';
 import 'package:test/test.dart';
 
-main() {
+void main() {
   group("Can parse from string", () {
     test("with HEAD method", () {
       // Arrange

test/models/retry_policy_test.dart

@@ -1,7 +1,7 @@
 import 'package:http_interceptor/http_interceptor.dart';
 import 'package:test/test.dart';
 
-main() {
+void main() {
   late RetryPolicy testObject;
 
   setUp(() {

test/utils/utils_test.dart

@@ -1,7 +1,7 @@
-import 'package:test/test.dart';
 import 'package:http_interceptor/utils/utils.dart';
+import 'package:test/test.dart';
 
-main() {
+void main() {
   group("buildUrlString", () {
     test("Adds parameters to a URL string without parameters", () {
       // Arrange