Don't set module version outside BCR (#4381)

**What type of PR is this?**

Bug fix

**What does this PR do? Why is it needed?**

This results in an empty version when rules_go is used as an override,
which should avoid the warning reported in
https://github.com/bazel-contrib/rules_go/issues/4380.

**Which issues(s) does this PR fix?**

Fixes #4380

**Other notes for review**