Dependabot cannot be upgraded to GitHub-native version due to unsupported `dep` package manager

Dependabot Preview will be shut down on August 3rd, 2021.

It appears that this repository has configured updates for `dep`.

The GitHub-native version of Dependabot does not support `dep`, which was [deprecated][deprecated] as of 2020.
Guidance from the `dep` maintainers is to upgrade to [go mod][go mod], which Dependabot [supports][supported ecosystems].

In order to keep getting updates for your Go dependencies, you'll need to migrate to `go mod` and add a [Dependabot configuration][Dependabot config file] for it to this repository.

[deprecated]: https://golang.github.io/dep/docs/introduction.html#:~:text=As%20of%202020%2C%20Dep%20is,official%20support%20since%20Go%201.11.&text=This%20is%20documentation%20for%20dep,tool%20for%20the%20Go%20language.
[go mod]: https://golang.org/ref/mod
[supported ecosystems]: https://docs.github.com/en/code-security/supply-chain-security/configuration-options-for-dependency-updates#package-ecosystem
[Dependabot config file]: https://docs.github.com/en/code-security/supply-chain-security/configuration-options-for-dependency-updates#about-the-dependabotyml-file

Inspect the repository's existing dep setup and Go dependency files first, then review the Dependabot configuration described in the issue. Confirm that the project uses go mod and that the resulting Dependabot configuration covers its Go dependencies.

Written by the indexing model from the issue text.