Bump Microsoft.CodeAnalysis.CSharp from 5.6.0 to 5.9.0

---
updated-dependencies:
- dependency-name: Microsoft.CodeAnalysis.CSharp
  dependency-version: 5.9.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

src/Exercism.TestRunner.CSharp/Exercism.TestRunner.CSharp.csproj

@@ -15,7 +15,7 @@
   <ItemGroup>
     <PackageReference Include="CommandLineParser" Version="2.9.1" />
     <PackageReference Include="Humanizer.Core" Version="3.0.10" />
-    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="5.6.0" />
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="5.9.0" />
   </ItemGroup>
 
 </Project>