fix: return PRs by last updated

[bcoe]

I don't believe merged_at was actually an option, based on reading docs, so I think we were just getting the default sort which was created .

[codecov]

Codecov Report

Merging #706 (879c182) into master (198c327) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #706   +/-   ##
=======================================
  Coverage   86.77%   86.77%           
=======================================
  Files          55       55           
  Lines        6579     6579           
  Branches      616      616           
=======================================
  Hits         5709     5709           
  Misses        869      869           
  Partials        1        1           

Impacted Files	Coverage Δ
src/github.ts	83.69% <100.00%> (ø)

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