[BUG] Execution fails when renaming the default Runner project

### :information_source: Info

Version: `e.g. v0.13.1`

### :speech_balloon: Description

Flutters [allows to rename the Runner.xcodeproj folder](https://github.com/flutter/flutter/pull/124533). If you do so, the execution of `flutter_launcher_icons` fails:

```
Unhandled exception:
PathNotFoundException: Cannot open file, path = 'ios/Runner.xcodeproj/project.pbxproj' (OS Error: No such file or directory, errno = 2)
#0 _checkForErrorResponse (dart:io/common.dart:55:9)
#1 _File.open. (dart:io/file_impl.dart:381:7)

#2 _File.readAsBytes. (dart:io/file_impl.dart:562:24)

#3 _File.readAsString (dart:io/file_impl.dart:621:18)

#4 LineSplitter.convert (dart:convert/line_splitter.dart:52:3)

#5 changeIosLauncherIcon (package:flutter_launcher_icons/ios.dart:149:30)

```

It would be nice, if this package does support renaming the Runner project as well.

Start at changeIosLauncherIcon in ios.dart:149, where the package attempts to read ios/Runner.xcodeproj/project.pbxproj. Reproduce the failure with an iOS project whose Runner.xcodeproj folder has been renamed, then verify that flutter_launcher_icons completes successfully with the renamed project.

Written by the indexing model from the issue text.