CI: add timeouts, add concurrency groups, remove duplicate PR builds

[DilumAluthge]

1. Add timeouts
2. Add concurrency groups - this will cancel old PR builds when new commits are pushed to a PR.
3. Remove duplicate PR builds (so that there isn't both a push and pull_request build on a PR)
4. Use the default job name generated by GitHub

[codecov]

Codecov Report

Base: 51.55% // Head: 51.55% // No change to project coverage 👍

Coverage data is based on head (ef3499d) compared to base (f453201).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #18   +/-   ##
=======================================
  Coverage   51.55%   51.55%           
=======================================
  Files           7        7           
  Lines         225      225           
=======================================
  Hits          116      116           
  Misses        109      109           

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