Bump ReportGenerator from 5.5.6 to 5.5.9

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

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

Author: dependabot[bot]

src/algorithm_exercises_csharp_test/algorithm_exercises_csharp_test.csproj

@@ -41,7 +41,7 @@
     <PackageReference Include="MSTest.TestAdapter" Version="4.2.1" />
     <PackageReference Include="MSTest.TestFramework" Version="4.2.1" />
     <PackageReference Include="Newtonsoft.Json" Version="13.0.4" />
-    <PackageReference Include="ReportGenerator" Version="5.5.6" />
+    <PackageReference Include="ReportGenerator" Version="5.5.9" />
   </ItemGroup>
 
   <!-- Exclude test project from coverage -->