Bump FluentAssertions from 6.8.0 to 6.9.0 (#326)

Bumps [FluentAssertions](https://github.com/fluentassertions/fluentassertions) from 6.8.0 to 6.9.0.
- [Release notes](https://github.com/fluentassertions/fluentassertions/releases)
- [Changelog](https://github.com/fluentassertions/fluentassertions/blob/develop/AcceptApiChanges.ps1)
- [Commits](fluentassertions/fluentassertions@6.8.0...6.9.0)

---
updated-dependencies:
- dependency-name: FluentAssertions
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

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

Author: dependabot[bot]

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

@@ -9,7 +9,7 @@
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
-    <PackageReference Include="FluentAssertions" Version="6.8.0" />
+    <PackageReference Include="FluentAssertions" Version="6.9.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.4.1" />
     <PackageReference Include="Moq" Version="4.18.4" />
     <PackageReference Include="xunit" Version="2.4.2" />