Roll out quantecon-book-theme v0.20.2 to all lecture sites

[mmcky]

quantecon-book-theme has been updated to v0.20.2 which includes:

• v0.20.2 — Fixed emphasis color on "et al." in textual citations (sphinxcontrib-bibtex author_year style)
• v0.20.1 — Initial citation emphasis fix + relaxed sphinxcontrib-bibtex upper bound to <3
• v0.20.0 — Language switcher for multilingual site support, SEO hreflang tags

Rollout status

• lecture-python.myst — update quantecon-book-theme to 0.20.2 lecture-python.myst#848
• lecture-python-programming
• lecture-python-advanced
• lecture-julia

Notes

The key fix is for the theme's emphasis styling (teal color on <em> elements) incorrectly applying to "et al." text in bibliography citations. This was most visible on pages using :cite:t: references with bibtex_reference_style: author_year.

Release: https://github.com/QuantEcon/quantecon-book-theme/releases/tag/v0.20.2