Repository: flutter
Issue: [go_router] Root routes require a `/` despite docs saying otherwise
Labels: waiting for customer response,in triage

### Steps to reproduce

The Changelog says:

>14.2.9 Relaxes route path requirements. Both root and child routes can now start with or without '/'.

But when I try this:

```dart
inal router = GoRouter(
  initialLocation: '/${LandingPage.routeName}',
  routes: [
    GoRoute(
      name: SplashPage.routeName,
      path: SplashPage.routeName,
      builder: (context, routerState) => const SplashPage(),
    ),
    GoRoute(
      name: LandingPage.routeName,
      path: LandingPage.routeName, // This is the string 'landing'
      builder: (context, routerState) => const LandingPage(),
      routes: [ .....]
```

I get a page saying `GoException: no routes for location: /landing`.

If I change the code to use `initialLocation: LandingPage.routeName,`, thus removing the `/`, I get an assertion error:

>'package:go_router/src/match.dart': Failed assertion: line 235 pos 12: 'uri.path.startsWith(newMatchedLocation)': is not true.

So I think this new feature is broken, or I am missing something here

I am using go_router version 14.6.3, confirmed on pubspec.lock.


### Expected results

The package would ignore the absence of a `/` in all route definitions.

### Actual results

I can only start my app if I declare my root routes with a `/` at their paths, as in:

```dart
final router = GoRouter(
  initialLocation: '/${LandingPage.routeName}',
  routes: [
    GoRoute(
      name: SplashPage.routeName,
      path: '/${SplashPage.routeName}',
      builder: (context, routerState) => const SplashPage(),
    ),
    GoRoute(
      name: LandingPage.routeName,
      path: '/${LandingPage.routeName}',
      builder: (context, routerState) => const LandingPage(),
      routes: [....]
```

### Code sample

See above

### Screenshots or Video

_No response_

### Logs

_No response_

### Flutter Doctor output

<details open><summary>Doctor output</summary>

```console
[✓] Flutter (Channel stable, 3.24.4, on macOS 15.1.1 24B91 darwin-arm64, locale en-AU)
    • Flutter version 3.24.4 on channel stable at /Users/michelfeinstein/.puro/envs/3.24.4/flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 603104015d (3 months ago), 2024-10-24 08:01:25 -0700
    • Engine revision db49896cf2
    • Dart version 3.5.4
    • DevTools version 2.37.3

[✓] Android toolchain - develop for Android devices (Android SDK version 35.0.0)
    • Android SDK at /Users/michelfeinstein/Library/Android/sdk
    • Platform android-35, build-tools 35.0.0
    • ANDROID_HOME = /Users/michelfeinstein/Library/Android/sdk
    • Java binary at: /opt/homebrew/Cellar/openjdk@17/17.0.13/libexec/openjdk.jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment Homebrew (build 17.0.13+0)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 16.2)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Build 16C5032a
    • CocoaPods version 1.16.2

[✓] Chrome - develop for the web
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 2024.2)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 21.0.4+-12422083-b607.1)

[✓] IntelliJ IDEA Community Edition (version 2024.1.1)
    • IntelliJ at /Applications/IntelliJ IDEA CE.app
    • Flutter plugin version 79.0.3
    • Dart plugin version 241.15989.9

[✓] VS Code (version 1.95.1)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.98.0

[✓] Connected device (6 available)
    • Snorlax (mobile)                • 00008027-001964DE212B002E            • ios            • iOS 17.7.1 21H216
    • Abra (mobile)                   • 00008112-000E18181E6BA01E            • ios            • iOS 18.1 22B83
    • iPhone 16 (mobile)              • 1A2D81B2-5F45-4F24-84B0-636DD475E1D6 • ios            • com.apple.CoreSimulator.SimRuntime.iOS-18-2 (simulator)
    • macOS (desktop)                 • macos                                • darwin-arm64   • macOS 15.1.1 24B91 darwin-arm64
    • Mac Designed for iPad (desktop) • mac-designed-for-ipad                • darwin         • macOS 15.1.1 24B91 darwin-arm64
    • Chrome (web)                    • chrome                               • web-javascript • Google Chrome 131.0.6778.266
    ! Device R5CW41Q82WT is not authorized.
      You might need to check your device for an authorization dialog.
    ! Error: Browsing on the local area network for Celebi. Ensure the device is unlocked and attached with a cable or associated with the same local area network as this Mac.
      The device must be opted into Developer Mode to connect wirelessly. (code -27)
    ! Error: Browsing on the local area network for iPhone. Ensure the device is unlocked and attached with a cable or associated with the same local area network as this Mac.
      The device must be opted into Developer Mode to connect wirelessly. (code -27)

[✓] Network resources
    • All expected network resources are available.

• No issues found!
```

</details>