fix: use modern PEP 723 syntax, fix mistake in name

[henryiii]

• I have added an entry to docs/changelog.md

Summary of changes

PEP 723 has been updated to use a scripts block and no run section. This updates to the new syntax, but still runs with the old syntax, producing a warning. This can be upgraded to an error (but with a nice message) later (or now, if you prefer, as it's still undocumented).

Edit: the old form used the wrong name (requirements instead of dependencies) so I went ahead and made it an error now. I can still do the soft deprecation instead though if that’s preferred.

Test plan

Tested by running

nox -s tests-3.11

There were 18 failures before this PR, and 18 after, so hoped that was good! :)

[dukecat0]

Please add a changelog entry.

[flying-sheep]

@henryiii would it be possible to make the tracebacks friendlier? Currently they show

Traceback (most recent call last):
  File "<string>", line 11, in <module>
ModuleNotFoundError: No module named 'requests'

Would be nice if that read File "actual-file-name.py", line 11, in __main__

[henryiii]

would it be possible to make the tracebacks friendlier?

I can look into that.