When we started generating custom modifiers into metadata format to support new function pointer APIs in #85504, we should have also added it to native layout format. We currently have a mismatch. This is a low risk bugfix to ignore modifiers on the metadata side. We'll want to do a full fix to actually emit and compare this. Tracked in a .NET 9 bug at #91381.

No regression test because I spent too much time being puzzled at why https://github.com/Handlebars-Net/Handlebars.Net/blob/50614fd844e5360eb10e76154aa74da4d7bf12ce/source/Handlebars/Helpers/IHelperDescriptor.cs#L13 is generated as a custom modifier (`[in] !TOptions& modreq([netstandard]System.Runtime.InteropServices.InAttribute) options`) whereas if I do it, I get `[in] !T& 'value'` with a custom attribute. We'll want to write a proper set of tests with ambiguities for the bug I opened anyway.