build(deps): bump Xamarin.AndroidX.Fragment in /src (#3068)

Bumps [Xamarin.AndroidX.Fragment](https://github.com/xamarin/AndroidX) from 1.3.6.3 to 1.3.6.4.
- [Release notes](https://github.com/xamarin/AndroidX/releases)
- [Commits](https://github.com/xamarin/AndroidX/commits)

---
updated-dependencies:
- dependency-name: Xamarin.AndroidX.Fragment
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

src/ReactiveUI.AndroidX/ReactiveUI.AndroidX.csproj

@@ -18,7 +18,7 @@
   <ItemGroup>
     <PackageReference Include="System.Runtime.Serialization.Primitives" Version="4.3.0" />
     <PackageReference Include="Xamarin.AndroidX.AppCompat" Version="1.3.1.3" />
-    <PackageReference Include="Xamarin.AndroidX.Fragment" Version="1.3.6.3" />
+    <PackageReference Include="Xamarin.AndroidX.Fragment" Version="1.3.6.4" />
     <PackageReference Include="Xamarin.AndroidX.Preference" Version="1.1.1.11" />
     <PackageReference Include="Xamarin.AndroidX.RecyclerView" Version="1.2.1.3" />
     <PackageReference Include="Xamarin.AndroidX.Lifecycle.LiveData" Version="2.3.1.3" />