Bump FluentAssertions and System.Threading.Tasks.Extensions (#634)

Bumps [FluentAssertions](https://github.com/fluentassertions/fluentassertions) and System.Threading.Tasks.Extensions. These dependencies needed to be updated together.

Updates `FluentAssertions` from 6.12.1 to 6.12.2
- [Release notes](https://github.com/fluentassertions/fluentassertions/releases)
- [Changelog](https://github.com/fluentassertions/fluentassertions/blob/develop/AcceptApiChanges.ps1)
- [Commits](fluentassertions/fluentassertions@6.12.1...6.12.2)

Updates `System.Threading.Tasks.Extensions` from 4.5.4 to 4.5.0

---
updated-dependencies:
- dependency-name: FluentAssertions
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: System.Threading.Tasks.Extensions
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

BitFaster.Caching.UnitTests.Std/BitFaster.Caching.UnitTests.Std.csproj

@@ -10,7 +10,7 @@
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
-    <PackageReference Include="FluentAssertions" Version="6.12.1" />
+    <PackageReference Include="FluentAssertions" Version="6.12.2" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
     <PackageReference Include="Moq" Version="4.20.70" />
     <PackageReference Include="ObjectLayoutInspector" Version="0.1.4" />

BitFaster.Caching.UnitTests/BitFaster.Caching.UnitTests.csproj

@@ -10,7 +10,7 @@
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
-    <PackageReference Include="FluentAssertions" Version="6.12.1" />
+    <PackageReference Include="FluentAssertions" Version="6.12.2" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
     <PackageReference Include="Moq" Version="4.20.69" />
     <PackageReference Include="ObjectLayoutInspector" Version="0.1.4" />