Incorrect rename of extra `type-comments`

[fmigneault]

The change introduced in ccc75d2 renamed the extra type-comments to type-comment (no s), causing mismatched warnings when installing with pip:

pip install "sphinx-autodoc-typehints[type_comments]<1.19"   # OK

pip install "sphinx-autodoc-typehints[type_comments]>=1.19" 
[...]
WARNING: sphinx-autodoc-typehints 1.19.4 does not provide the extra 'type_comments'
[...]