Bump FluentAssertions and Microsoft.NETFramework.ReferenceAssemblies in /Source (#354)

Bump FluentAssertions and Microsoft.NETFramework.ReferenceAssemblies

Bumps [FluentAssertions](https://github.com/fluentassertions/fluentassertions) and [Microsoft.NETFramework.ReferenceAssemblies](https://github.com/Microsoft/dotnet). These dependencies needed to be updated together.

Updates `FluentAssertions` from 6.12.0 to 8.1.1
- [Release notes](https://github.com/fluentassertions/fluentassertions/releases)
- [Changelog](https://github.com/fluentassertions/fluentassertions/blob/main/AcceptApiChanges.ps1)
- [Commits](fluentassertions/fluentassertions@6.12.0...8.1.1)

Updates `Microsoft.NETFramework.ReferenceAssemblies` from 1.0.3 to 1.0.3
- [Commits](https://github.com/Microsoft/dotnet/commits)

---
updated-dependencies:
- dependency-name: FluentAssertions
  dependency-type: direct:production
  update-type: version-update:semver-major
- dependency-name: Microsoft.NETFramework.ReferenceAssemblies
  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]

Source/EasyNetQ.Management.Client.IntegrationTests/EasyNetQ.Management.Client.IntegrationTests.csproj

@@ -13,7 +13,7 @@
 
   <ItemGroup>
     <PackageReference Include="EasyNetQ" Version="8.0.0-beta96" />
-    <PackageReference Include="FluentAssertions" Version="6.12.0" />
+    <PackageReference Include="FluentAssertions" Version="8.1.1" />
     <PackageReference Include="docker.dotnet" Version="3.125.15" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.13.0" />
     <PackageReference Include="xunit" Version="2.8.1" />

Source/EasyNetQ.Management.Client.Tests/EasyNetQ.Management.Client.Tests.csproj

@@ -18,7 +18,7 @@
 
   <ItemGroup>
     <PackageReference Include="System.Text.Json" Version="8.0.5" />
-    <PackageReference Include="FluentAssertions" Version="6.12.0" />
+    <PackageReference Include="FluentAssertions" Version="8.1.1" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.13.0" />
     <PackageReference Include="xunit" Version="2.8.1" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.8.1">