Cancel concurrent workflows

[akaszynski]

Problem

Change the GitHub actions CI/CD to cancel old workflows when a new commit that supersedes the old one. For example:

• You open a PR.
• Immediately determine something is broken (e.g. style guide or unit tests fail).
• Submit a new PR.
• Old workflows are still on-going (like docs).

While we don't pay for the actions, it does mean that new workflows have to wait if we end up saturating GitHub.

Solution

Simply set cancel-in-progress to true for concurrency. For details, see Using Concurrency.

[codecov]

Codecov Report

Merging #2835 (56769cb) into main (b699868) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #2835   +/-   ##
=======================================
  Coverage   94.02%   94.02%           
=======================================
  Files          76       76           
  Lines       16405    16405           
=======================================
  Hits        15425    15425           
  Misses        980      980           

[MatthewFlamm]

LGTM

[adeak]

Great idea, thanks. This has always seemed weird to me. Now we only have to watch out when we want to prove that a given test breaks before the fix is pushed :)