Fix docstring markup in sage/doctest #34162
Description
Part of #34157:
sage/doctest/sources.py:193:1: RST215 Inline interpreted text or phrase reference start-string without end-string.
sage/doctest/sources.py:239:1: RST215 Inline interpreted text or phrase reference start-string without end-string.
sage/doctest/sources.py:429:1: RST201 Block quote ends without a blank line; unexpected unindent.
sage/doctest/sources.py:431:1: RST201 Block quote ends without a blank line; unexpected unindent.
sage/doctest/sources.py:765:1: RST214 Inline literal start-string without end-string.
sage/doctest/sources.py:765:1: RST214 Inline literal start-string without end-string.
Component: documentation
Author: Frédéric Chapoton
Branch/Commit: d7ab884
Reviewer: Matthias Koeppe
Issue created by migration from https://trac.sagemath.org/ticket/34162