⬆️ UPGRADE: Change Sphinx pinning to allow version 4

[astrojuanlu]

Sphinx 4.0.0b2 beta is out, and it would be great to see if MyST-Parser works with it. I am doing some local tests with https://github.com/poliastro/poliastro/, which uses it.

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[codecov]

Codecov Report

Merging #362 (981b843) into master (cb0bca0) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #362   +/-   ##
=======================================
  Coverage   90.61%   90.61%           
=======================================
  Files          14       14           
  Lines        1833     1833           
=======================================
  Hits         1661     1661           
  Misses        172      172           

Flag	Coverage Δ
pytests	90.61% <ø> (ø)

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[chrisjsewell]

thanks, but I can say for definite there are things to address like executablebooks/meta#306 (comment)

[astrojuanlu]

Woops, I didn't see that discussion, will take a look. Thanks @chrisjsewell!

[jpmckinney]

Can we unpin and later fix mathjax issues? Not everyone who uses MyST-Parser (but who wants to use Sphinx 4) uses mathjax. It can be a minor version to flag that the upgrade isn't seamless.

[chrisjsewell]

superceded by #390