Enable go toolchain directive in go.mod after FOSSA action starts supporting it

[pmalek]

Problem statement

FOSSA action - https://github.com/fossas/fossa-action - doesn't seem to support go 1.21's toolchain directive:

      Error parsing file: /home/runner/work/kubernetes-ingress-controller/kubernetes-ingress-controller/go.mod.

          /home/runner/work/kubernetes-ingress-controller/kubernetes-ingress-controller/go.mod:5:1:
            |
          5 | toolchain go1.21.0
            | ^
          unexpected 't'
          expecting "exclude", "go", "replace", "require", "retract", or end of input

https://github.com/Kong/kubernetes-ingress-controller/actions/runs/6141226981/job/16661215380

This issue tracks the effort of bringing it back after FOSSA starts supporting toolchain in go.mod.

Special notes

Related upstream issue:

fossas/fossa-action#33