go_repository_cache: set GOTOOLCHAIN to 'local' (#1859)

**What type of PR is this?**

Bug fix

**What package or component does this PR mostly affect?**

go_repository_cache

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

Override the **GOTOOLCHAIN** local environment parameter defined by `go
env -w` to use the local Go environment made available by `gazelle`.

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

Fixes #1858

**Other notes for review**

Same fix than https://github.com/bazelbuild/rules_go/pull/3660 in
[rules_go](https://github.com/bazelbuild/rules_go).