chore(deps): Bump StyleCop.Analyzers.Unstable in /src

Bumps [StyleCop.Analyzers.Unstable](https://github.com/DotNetAnalyzers/StyleCopAnalyzers) from 1.2.0.507 to 1.2.0.556.
- [Release notes](https://github.com/DotNetAnalyzers/StyleCopAnalyzers/releases)
- [Changelog](https://github.com/DotNetAnalyzers/StyleCopAnalyzers/blob/master/documentation/KnownChanges.md)
- [Commits](https://github.com/DotNetAnalyzers/StyleCopAnalyzers/commits)

---
updated-dependencies:
- dependency-name: StyleCop.Analyzers.Unstable
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

src/Directory.Build.props

@@ -21,7 +21,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="StyleCop.Analyzers.Unstable" Version="1.2.0.507" PrivateAssets="all" />
+    <PackageReference Include="StyleCop.Analyzers.Unstable" Version="1.2.0.556" PrivateAssets="all" />
     <PackageReference Include="Microsoft.CodeAnalysis.NetAnalyzers" Version="7.0.4" PrivateAssets="all" />
     <PackageReference Include="Microsoft.CodeAnalysis.CSharp.CodeStyle" Version="3.11.0" PrivateAssets="all" />
     <PackageReference Include="CSharpIsNullAnalyzer" Version="0.1.495" PrivateAssets="all" />