Update pyproject.toml - replace `output_formatting` with `output-formatting`
closes #55290

Simply said, none of this would work (dependencies from `output-formatting` would not be installed):

```
pip install pandas[output-formatting]
pip install pandas[output_formatting]
pip install pandas[output-formatting,xml]
```

When being distributed, underscores are replaces with dashes. So, in the packaged PKG-INFO file you won't find spots of `output_formatting`, but only `output-formatting`:

```
Requires-Dist: lxml>=4.8.0; extra == "xml"
Requires-Dist: jinja2>=3.1.2; extra == "output-formatting"
Requires-Dist: tabulate>=0.8.10; extra == "output-formatting"
```

But on the same time, this:

```
Provides-Extra: output_formatting
```

This fix addresses that.
Thanks could you add a whatsnew note in `2.1.2.rst`? @mroeschke:

Done. Could you also change the references in `doc/source/getting_started/install.rst` and `.github/workflows/package-checks.yml`? @mroeschke:

Done. Thanks @barseghyanartur 