Fix docstring markup in sage/plot and sage/graphs #34164
Description
Part of #34157:
sage/plot/polygon.py:99:1: RST215 Inline interpreted text or phrase reference start-string without end-string.
sage/plot/polygon.py:113:1: RST215 Inline interpreted text or phrase reference start-string without end-string.
sage/graphs/dot2tex_utils.py:89:1: RST201 Block quote ends without a blank line; unexpected unindent.
sage/graphs/dot2tex_utils.py:91:1: RST301 Unexpected indentation.
sage/graphs/graph_plot.py:50:1: RST299 The "csv-table" directive requires content; none supplied.
Component: documentation
Author: Frédéric Chapoton
Branch/Commit: c088449
Reviewer: Matthias Koeppe
Issue created by migration from https://trac.sagemath.org/ticket/34164