Bump FluentAssertions from 6.11.0 to 6.12.0 in /eng/dependabot

Bumps [FluentAssertions](https://github.com/fluentassertions/fluentassertions) from 6.11.0 to 6.12.0.
- [Release notes](https://github.com/fluentassertions/fluentassertions/releases)
- [Changelog](https://github.com/fluentassertions/fluentassertions/blob/develop/AcceptApiChanges.ps1)
- [Commits](fluentassertions/fluentassertions@6.11.0...6.12.0)

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

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

eng/dependabot/Packages.props

@@ -22,7 +22,7 @@
 
     <!--Test dependencies-->
     <PackageReference Update="FakeItEasy" Version="7.4.0" />
-    <PackageReference Update="FluentAssertions" Version="6.11.0" />
+    <PackageReference Update="FluentAssertions" Version="6.12.0" />
     <PackageReference Update="Microsoft.NET.Test.Sdk" Version="17.7.1" />
     <PackageReference Update="xunit.abstractions" Version="2.0.3" />
     <PackageReference Update="Newtonsoft.Json.Schema" Version="3.0.14" />