Buildpack does no longer work in online version when setting `GOTOOLCHAIN=local`

[silvestre]

When setting GOTOOLCHAIN=local which you might want to set to not allow Go to download itself, the buildpack stopped working after #516 as the go.mod requires a Go > 1.23 but the install_go.sh script still downloads Go 1.22:

   2025-08-18T17:48:52.53+0200 [STG/0] OUT -----> Download go 1.22.5
   2025-08-18T17:48:55.77+0200 [STG/0] OUT -----> Running go build supply
   2025-08-18T17:48:55.77+0200 [STG/0] OUT /tmp/buildpackdownloads/45909db73807128d ~
   2025-08-18T17:48:55.77+0200 [STG/0] ERR go: go.mod requires go >= 1.23.0 (running go 1.22.5; GOTOOLCHAIN=local)
   2025-08-18T17:48:55.77+0200 [STG/0] ERR Failed to compile droplet: Failed to run all supply scripts: exit status 1

I suppose the script updating the Go version in go.mod should update install_go.sh as well.

#525 fixes it for now, by bumping the downloaded version to the latest currently in manifest.yml