Update dependency System.Collections.Immutable to v9

Author: renovate-bot

EnumerableAsyncProcessor/EnumerableAsyncProcessor.csproj

@@ -32,7 +32,7 @@
     </ItemGroup>
 
     <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
-        <PackageReference Include="System.Collections.Immutable" Version="8.0.0" />
+        <PackageReference Include="System.Collections.Immutable" Version="9.0.0" />
         <PackageReference Include="Microsoft.Bcl.AsyncInterfaces" Version="8.0.0" />
         <PackageReference Include="morelinq" Version="4.3.0" />