[MRG] update CI for latest branch name change

[luizirber]

Turns out the master->latest transition didn't touch CI. Oops!

TODO

• schedule all checks to run on master every day for GitHub Actions (like it works in travis)
• Update all places mentioning master (badges in README, binder links, docs...)

Checklist

• Is it mergeable?
• make test Did it pass the tests?
• make coverage Is the new code covered?
• Did it change the command-line interface? Only additions are allowed
  without a major version increment. Changing file formats also requires a
  major version number increment.
• Was a spellchecker run on the source code and documentation after
  changes were made?

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (latest@f4fac4b). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             latest    #1150   +/-   ##
=========================================
  Coverage          ?   83.72%           
=========================================
  Files             ?       95           
  Lines             ?     9012           
  Branches          ?        0           
=========================================
  Hits              ?     7545           
  Misses            ?     1467           
  Partials          ?        0           

Flag	Coverage Δ
#rusttests	67.86% <0.00%> (?)

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[luizirber]

Ready for review and merge when checks are passing @ctb

[ctb]

Looks good, overall. Question: do we want to point at stable URLs for documentation, notebooks, etc? I expect we'll keep stable up to date with the last release, in the future...

[luizirber]

Looks good, overall. Question: do we want to point at stable URLs for documentation, notebooks, etc? I expect we'll keep stable up to date with the last release, in the future...

I thought stable was temporary until 4.0.0 is released, keep syncing branches will be annoying... Maybe turn stable into a tag, and add to the release notes to replace it on every stable release?