This updates github.com/rogpeppe/go-internal from 1.6.1 to 1.8.0
and the github action 'setup-go' from v1 to v2.

It also adds a config file for dependabot to automatically check
this repo for new dependency versions weekly.

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 3.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v2...v3)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

This handles a few cases (similar to how fmt %#v does):

- A GoString method on a value receiver, called with a nil pointer
- A GoString method on a pointer receiver that doesn't check for nil
- A GoString method that panics in some other way

Because Go 1.17 added a method Time.GoString with value receiver, this
broke structs that had *time.Time fields with nil values (which is
common!).

Also added a bunch of tests for these cases.

Fixes kr#77

Co-authored-by: Jordan Barrett <[email protected]>

This change bumps github.com/rogpeppe/go-internal from version 1.8.0 to 1.9.0.

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Sync with master first to refresh go.mod / go.sum and run tests again,
before merging PR.