Fix the install_requires used in test_dist_info to use the dangling
syntax, in order to correctly handle markers.  This fixes syntax error
when parsed by packaging-22.0+, as well as setuptools warning:

```
UserWarning: One of the parsed requirements in `install_requires` looks like a valid environment marker: \'sys_platform != "linux"\'
Make sure that the config is correct and check https://setuptools.pypa.io/en/latest/userguide/declarative_config.html#opt-2
  warnings.warn(msg, UserWarning)\n'
```

During a PEP 517 build, this directory can later be passed to
``build_py`` via the ``existing_egg_info_dir attribute``
(which in turn avoids re-running ``egg_info`` to create a manifest).