Bump sphinx-rtd-theme from 1.2.0 to 1.2.1 in /docs/readthedocs (#816)

Author: dependabot[bot]

docs/readthedocs/requirements.txt

@@ -1,6 +1,6 @@
 commonmark==0.9.1
 recommonmark==0.7.1
 Sphinx==5.3.0
-sphinx-rtd-theme==1.2.0
+sphinx-rtd-theme==1.2.1
 myst-parser==1.0.0
 markdown-it-py==2.2.0