As described in
https://www.ruby-lang.org/en/news/2020/12/25/ruby-3-0-0-released/, Ruby
3.0.0 promoted net-http and net-imap from stdlib. Adding net-http as a
dependency avoids "already initialized constant errors" if net-imap or
some other gem is included. uri is needed as well for a similar reason.

uri needs to be locked down because bundler v2.1.4 isn't happy with
v0.10.1 (https://gitlab.com/gitlab-org/gitlab/-/jobs/1114901581):

```
Gem::LoadError: You have already activated uri 0.10.0, but your
Gemfile requires uri 0.10.1. Since uri is a default gem, you can either
remove your dependency on it or try updating to a newer version of
bundler that supports uri as a default gem.
```