Bump ReportGenerator from 5.2.4 to 5.5.9

---
updated-dependencies:
- dependency-name: ReportGenerator
  dependency-version: 5.5.9
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

test/GuardClauses.UnitTests/GuardClauses.UnitTests.csproj

@@ -18,7 +18,7 @@
         </PackageReference>
 
         <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.9.0" />
-        <PackageReference Include="ReportGenerator" Version="5.2.4" />
+        <PackageReference Include="ReportGenerator" Version="5.5.9" />
         <PackageReference Include="xunit" Version="2.7.1" />
         <PackageReference Include="xunit.runner.visualstudio" Version="2.5.8">
           <PrivateAssets>all</PrivateAssets>