chore(deps): update dependency icsharpcode.decompiler to v9

Author: renovate[bot]

src/ReactiveMarbles.SourceGenerator.TestNuGetHelper/ReactiveMarbles.SourceGenerator.TestNuGetHelper.csproj

@@ -9,6 +9,6 @@
   <ItemGroup>
     <PackageReference Include="ReactiveMarbles.NuGet.Helpers" Version="1.1.1" />
     <PackageReference Include="Microsoft.CodeAnalysis.CSharp.Workspaces" Version="4.0.1" />
-    <PackageReference Include="ICSharpCode.Decompiler" Version="8.2.0.7535" />
+    <PackageReference Include="ICSharpCode.Decompiler" Version="9.1.0.7988" />
   </ItemGroup>
 </Project>