build(deps): bump System.Reactive from 5.0.0 to 6.0.0 in /src (#844)

Bumps [System.Reactive](https://github.com/dotnet/reactive) from 5.0.0 to 6.0.0.
- [Release notes](https://github.com/dotnet/reactive/releases)
- [Commits](https://github.com/dotnet/reactive/commits)

---
updated-dependencies:
- dependency-name: System.Reactive
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

src/Akavache.Core/Akavache.Core.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="MSBuild.Sdk.Extras">
+<Project Sdk="MSBuild.Sdk.Extras">
   <PropertyGroup>
     <TargetFrameworks>netstandard2.0;netstandard2.1;Xamarin.iOS10;Xamarin.Mac20;Xamarin.TVOS10;MonoAndroid12.0;MonoAndroid12.1;MonoAndroid13.0;tizen40;net6.0;net6.0-android;net6.0-ios;net6.0-tvos;net6.0-macos;net6.0-maccatalyst;net7.0;net7.0-android;net7.0-ios;net7.0-tvos;net7.0-macos;net7.0-maccatalyst</TargetFrameworks>
     <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">$(TargetFrameworks);net462;net6.0-windows10.0.17763.0;net7.0-windows10.0.17763.0</TargetFrameworks>
@@ -12,7 +12,7 @@
   <ItemGroup>
     <PackageReference Include="Newtonsoft.Json" Version="13.0.3" />
     <PackageReference Include="Newtonsoft.Json.Bson" Version="1.0.2" />
-    <PackageReference Include="System.Reactive" Version="5.0.0" />
+    <PackageReference Include="System.Reactive" Version="6.0.0" />
     <PackageReference Include="Splat" Version="14.*" />
   </ItemGroup>
 

src/Akavache.Sqlite3/Akavache.Sqlite3.csproj

@@ -19,7 +19,7 @@
 
   <ItemGroup>
     <PackageReference Include="SQLitePCLRaw.core" Version="2.1.5" />
-    <PackageReference Include="System.Reactive" Version="5.0.0" />
+    <PackageReference Include="System.Reactive" Version="6.0.0" />
     <PackageReference Include="Splat" Version="14.*" />
   </ItemGroup>