This was not intended to be supported, and it has resulted in calls as `absl::StrCat({...})`, which are not supported and only work coincidentally for the first 4 arguments due to `absl::StrCat` having overloads that take `absl::AlphaNum` directly for those.

The existing situation prevents modifying the implementations of such functions to alternatives that do not have such overloads for those arguments.

PiperOrigin-RevId: 599872755
Change-Id: I02c90119b2b96a922cf7e3b5d5f02affe24a272d