[Go >=1.21+] Log the actual toolchain to be used for a given module instead of the pre-installed toolchain

[eskultety]

Currently, we're reporting the toolchain we selected to process a project, e.g. 1.21.0 (pre-installed) but that toolchain might not end being the one to be used for the given project as the project may specify any micro release for the toolchain it desires (e.g. 1.21.8) which we're currently handling by passing GOTOOLCHAIN=auto to the underlying Go process which will first download the desired toolchain and then process the requested command (and project) with it.
We should ideally report the target toolchain that we're invoking instead of the intermediary toolchain that will just download the target one.