Black doesn't warn about long lines inside function docstrings

[MVrachev]

Description of issue or feature request: After we merged #1815 I noticed multiple lines inside function docstrings are over 80 characters. Then I run a local scan with black (version 22.1.0) and I thought black will raise an error or format them, but nothing happened. Then, I proceeded to delete my local tox cache and run tox -e lint, but nothing happen again.

Some examples of long lines inside tuf/api/metadata.py:

• https://github.com/theupdateframework/python-tuf/blob/d4dd652582d7c9b67421b1effc82f462d63801d1/tuf/api/metadata.py#L619
• https://github.com/theupdateframework/python-tuf/blob/d4dd652582d7c9b67421b1effc82f462d63801d1/tuf/api/metadata.py#L763
• 1138 -1142: https://github.com/theupdateframework/python-tuf/blob/d4dd652582d7c9b67421b1effc82f462d63801d1/tuf/api/metadata.py#L1138
• https://github.com/theupdateframework/python-tuf/blob/d4dd652582d7c9b67421b1effc82f462d63801d1/tuf/api/metadata.py#L1251

Note that when there are long lines with normal code black does raise an error or format them.