Thank you for raising this, this is an issue we're aware of, and we're currently working on a fix for it. Until that fix is available, I would suggest the following possible approaches to work around the issue:
In your project options, you can add an additional mtouch argument to the iOS Build options. If you add the argument
--registrar:legacythen the project will be configured to use the old Xamarin type registration system, which is less strict and will not throw an error in this case.
If you don't need the latest version of ShinobiGrids, you could go back to using the previous version (2.5.3). The Pull to Action control was only added to Grids in the last release, so using 2.5.3 would get rid of the type collision.
We are currently working on a fix for this issue, which will remove the need for either of these workarounds. Once the fix is released, we shall post up here to let you know.