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] <[email protected]>

Author: dependabot[bot]

test/Microsoft.OpenApi.Readers.Tests/Microsoft.OpenApi.Readers.Tests.csproj

@@ -243,7 +243,7 @@
 
     <ItemGroup>
         <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.0.0" />
-        <PackageReference Include="FluentAssertions" Version="6.3.0">
+        <PackageReference Include="FluentAssertions" Version="6.4.0">
         </PackageReference>
         <PackageReference Include="Newtonsoft.Json" Version="13.0.1">
         </PackageReference>

test/Microsoft.OpenApi.Tests/Microsoft.OpenApi.Tests.csproj

@@ -15,7 +15,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="FluentAssertions" Version="6.3.0" />
+    <PackageReference Include="FluentAssertions" Version="6.4.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.0.0" />
     <PackageReference Include="Newtonsoft.Json" Version="13.0.1" />
     <PackageReference Include="SharpYaml" Version="1.8.0" />