Fix linking submodule of go workspace

[timebertt]

Proposed Changes

• when linking go src to the vgopath, we skip symlinking directories which contain other submodules

Fixes #26

Example result (using the reproduction steps from the issue):

$ pwd
/tmp/workspace
$ mkdir tmp && vgopath -o tmp
$ tree
.
├── go.mod # example.dev/main
├── go.work # use both example.dev/main and example.dev/main/sub
├── sub
│  └── go.mod # example.dev/main/sub
└── tmp
   ├── bin -> /Users/ebertti/go/bin
   ├── pkg -> /Users/ebertti/go/pkg
   └── src
      └── example.dev
         └── main
            ├── go.mod -> /tmp/workspace/go.mod
            ├── go.work -> /tmp/workspace/go.work
            ├── sub
            │  └── go.mod -> /tmp/workspace/sub/go.mod
            └── tmp -> /tmp/workspace/tmp

Verified with timebertt/kubernetes-controller-sharding#228 and gardener/gardener@abf64b6.

[timebertt]

@afritzler I think this scenario used to work (1829a8f#diff-67213f39b84a013e7db04664cd3ad943b7a237d97b9c6e862d10806ac27def28R209-R210) but might have been broken by 2520e6a#diff-b94d4322eb20f9cd90dc342d084155e9a360a54d58e2ee74170a73c80a967d42R108-R109.

This PR is a more general solution that works independently of whether modules have a version assigned.

[afritzler]

Thanks @timebertt for the PR. I updated here the Golang version and did some other project housekeeping. Lets merge that and rebase this PR with those changes.

/ref #28

[timebertt]

Lovely, rebase done :)

[timebertt]

Thanks for the prompt release @afritzler!