This is incorrect afaict. The Go docs specify that the toolchain directive is only considered in the "main" module. If your dependencies set it, it has no effect (unless they're binary tool dependencies that you go install).
A module’s go line must declare a version greater than or equal to the go version declared by each of the
modules listed in require statements. A workspace’s go line must declare a version greater than or equal
to the go version declared by each of the modules listed in use statements.
For example, if module M requires a dependency D with a go.mod that declares go 1.22.0, then M’s go.mod
cannot say go 1.21.3.