[golang.cgo_tool_search_paths] started throwing on <ASDF> and <ASDF_LOCAL> placeholders

[jgranstrom]

Describe the bug
<ASDF> and <ASDF_LOCAL> placeholders for system paths in pants.toml at [golang.cgo_tool_search_paths] started breaking recently. I think it might have been around here e891b87.

I understand it's not supposed to be supported there but it went from being ignored to throwing, and the error is not describing which configuration is the culprit, and many could reference <ASDF>.

Can we improve the error message or otherwise include the fact in the changelog possibly?

Pants version
main branch, ~2.25

OS
MacOS

Additional info

native_engine.IntrinsicError: path_metadata_request error: path for PathNamespace.SYSTEM must an absolute path. Instead, got `<ASDF>`