Bump FluentAssertions from 5.10.3 to 6.12.0

Bumps [FluentAssertions](https://github.com/fluentassertions/fluentassertions) from 5.10.3 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@5.10.3...6.12.0)

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

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

src/Directory.Build.props

@@ -20,7 +20,7 @@
     <NetFrameworkTestVersion>net48</NetFrameworkTestVersion>
     <XunitVersion>2.7.0</XunitVersion>
     <XunitRunnerVersion>2.5.7</XunitRunnerVersion>
-    <FluentAssertionsVersion>5.10.3</FluentAssertionsVersion>
+    <FluentAssertionsVersion>6.12.0</FluentAssertionsVersion>
     <TestSdkVersion>17.9.0</TestSdkVersion>
     <NBenchVersion>2.0.1</NBenchVersion>
     <HyperionVersion>0.9.16</HyperionVersion>