Improve override error note for LSP violations

[dhruvmal128]

Fixes #7994.

Adds a note explaining that incompatible method overrides violate the Liskov substitution principle. The existing error is preserved; this change only adds an explanatory note.

Testing:

• Ran python -m mypy /tmp/lsp_test.py before/after
• python runtests.py self
• python runtests.py lint

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

steam.py (https://github.com/Gobot1234/steam.py)
+ steam/ext/csgo/client.py:55: note: This violates the Liskov substitution principle
+ steam/ext/tf2/client.py:52: note: This violates the Liskov substitution principle

discord.py (https://github.com/Rapptz/discord.py)
+ discord/invite.py:518: note: This violates the Liskov substitution principle
+ discord/channel.py:392: note: This violates the Liskov substitution principle
+ discord/channel.py:1544: note: This violates the Liskov substitution principle
+ discord/channel.py:1810: note: This violates the Liskov substitution principle
+ discord/channel.py:2079: note: This violates the Liskov substitution principle
+ discord/channel.py:2508: note: This violates the Liskov substitution principle
+ discord/ui/select.py:492: note: This violates the Liskov substitution principle
+ discord/ui/select.py:666: note: This violates the Liskov substitution principle
+ discord/ui/select.py:774: note: This violates the Liskov substitution principle
+ discord/ui/select.py:878: note: This violates the Liskov substitution principle
+ discord/ui/select.py:1007: note: This violates the Liskov substitution principle

Tanjun (https://github.com/FasterSpeeding/Tanjun)
+ tanjun/context/slash.py:1035: note: This violates the Liskov substitution principle
+ tanjun/context/message.py:134: note: This violates the Liskov substitution principle
+ tanjun/context/menu.py:102: note: This violates the Liskov substitution principle

jax (https://github.com/google/jax)
+ jax/_src/prng.py:348: note: This violates the Liskov substitution principle

apprise (https://github.com/caronc/apprise)
+ apprise/plugins/viber.py:181: note: This violates the Liskov substitution principle
+ apprise/plugins/mattermost.py:702: note: This violates the Liskov substitution principle
+ apprise/plugins/fluxer.py:857: note: This violates the Liskov substitution principle
+ apprise/plugins/discord.py:696: note: This violates the Liskov substitution principle
+ apprise/plugins/xmpp/base.py:296: note: This violates the Liskov substitution principle
+ apprise/plugins/xmpp/base.py:429: note: This violates the Liskov substitution principle
+ apprise/plugins/irc/base.py:392: note: This violates the Liskov substitution principle