Using knative.dev/toolbox for older versions of Golang is broken

[cardil]

hack/library.sh

Line 751 in 70d4b00

done < <(go_run knative.dev/toolbox/modscope@latest ls -p)

The referenced code means the latest version of the toolbox is being used, no matter the current Golang installation. If called for, an older branch (for example, rebuiling release-1.16), while keeping the older version of Golang, will fail, because toolbox Go version might be higher.

It leads to errors like:

go: downloading knative.dev/toolbox v0.0.0-20250612145048-e9fe9e820228
go: knative.dev/toolbox/modscope@latest: knative.dev/toolbox@v0.0.0-20250612145048-e9fe9e820228 requires go >= 1.23.0 (running go 1.22.9; GOTOOLCHAIN=local) 

/kind bug

[cardil]

It is used in a bunch of places: https://github.com/search?q=repo%3Aknative%2Fhack%20%22knative.dev%2Ftoolbox%22&type=code

[cardil]

/assign