Bump ReportGenerator from 5.1.18 to 5.1.20

Bumps [ReportGenerator](https://github.com/danielpalme/ReportGenerator) from 5.1.18 to 5.1.20.
- [Release notes](https://github.com/danielpalme/ReportGenerator/releases)
- [Commits](danielpalme/ReportGenerator@v5.1.18...v5.1.20)

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

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

Author: dependabot[bot]

test/GuardClauses.UnitTests/GuardClauses.UnitTests.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
         <TargetFramework>net6.0</TargetFramework>
@@ -17,7 +17,7 @@
             <PrivateAssets>all</PrivateAssets>
         </PackageReference>
         <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.5.0" />
-        <PackageReference Include="ReportGenerator" Version="5.1.18" />
+        <PackageReference Include="ReportGenerator" Version="5.1.20" />
         <PackageReference Include="xunit" Version="2.4.2" />
         <PackageReference Include="xunit.runner.visualstudio" Version="2.4.5" />
     </ItemGroup>