then asking for the old pre-Go 1.21 `panic(nil)` behavior and the
new Go 1.23 `asynctimerchan=0` behavior.

Only the work module's `go.mod` is consulted for `godebug` directives.
Any directives in required dependency modules are ignored.
It is an error to list a `godebug` with an unrecognized setting.
(Toolchains older than Go 1.23 reject all `godebug` lines, since they do not
understand `godebug` at all.)