Bump FluentAssertions from 6.3.0 to 6.4.0

Bumps [FluentAssertions](https://github.com/fluentassertions/fluentassertions) from 6.3.0 to 6.4.0.
- [Release notes](https://github.com/fluentassertions/fluentassertions/releases)
- [Changelog](https://github.com/fluentassertions/fluentassertions/blob/master/AcceptApiChanges.ps1)
- [Commits](fluentassertions/fluentassertions@6.3.0...6.4.0)

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

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

test/Cosmos.Abstracts.Tests/Cosmos.Abstracts.Tests.csproj

@@ -14,7 +14,7 @@
 
   <ItemGroup>
     <PackageReference Include="DataGenerator" Version="5.0.0.178" />
-    <PackageReference Include="FluentAssertions" Version="6.3.0" />
+    <PackageReference Include="FluentAssertions" Version="6.4.0" />
     <PackageReference Include="MartinCostello.Logging.XUnit" Version="0.2.0" />
     <PackageReference Include="Microsoft.Extensions.Configuration.EnvironmentVariables" Version="6.0.0" />
     <PackageReference Include="Microsoft.Extensions.Configuration.Json" Version="6.0.0" />