Set AST node fallback end_lineno & end_col_offset as well

[mgorny]

When setting the fallback values for lineno & col_offset, set them
also for end_lineno & end_col_offset. This fixes a regression
in Python 3.11.0b2 where lineno without end_lineno would cause
an exception to be thrown.

Fixes #2425

Checklist:

• Add tests that demonstrate the correct behavior of the change. Tests should fail without the change.
• Add or update relevant docs, in the docs folder and in code.
• Add an entry in CHANGES.rst summarizing the change and linking to the issue.
• Add .. versionchanged:: entries in any relevant code docs.
• Run pre-commit hooks and fix any issues.
• Run pytest and tox, no tests failed.

[mgorny]

The py3.11 failures don't seem to be caused by my changes.

I think the mypy failure is because it doesn't include up-to-date typing data for the ast module. Since the attrs are set conditionally to node._attributes, I don't think that's a real issue. However, I don't know mypy enough to know how to solve this.

[mgorny]

Thanks!