Usually, developers run a single test locally.
Disabling eager loading by default in test environment should increase
productivity since it saves around 10 seconds:

With `eager_load` as `true`:
```bash
bogdanvlviv@lenovo:~/gitlab-development-kit/gitlab$ bin/rspec spec/models/users_statistics_spec.rb
Run options: include {:focus=>true}

All examples were filtered out; ignoring {:focus=>true}

Test environment set up in 5.122837013 seconds
......

Finished in 8.51 seconds (files took 16.46 seconds to load)
6 examples, 0 failures
```

With `eager_load` as `false`:
```bash
bogdanvlviv@lenovo:~/gitlab-development-kit/gitlab$ bin/rspec spec/models/users_statistics_spec.rb
Run options: include {:focus=>true}

All examples were filtered out; ignoring {:focus=>true}

Test environment set up in 5.013345478 seconds
......

Finished in 8.24 seconds (files took 7.18 seconds to load)
6 examples, 0 failures
```

Inspired by https://github.com/rails/rails/pull/43508...