ci: use node.js version from matrix

[dnalborczyk]

fixes: #530 (comment)

also included node.js v15

v10 can probably dropped end-of-April: https://nodejs.org/en/about/releases/ and replaced with v16 (while v15 to be removed)

[codecov]

Codecov Report

Merging #539 (0b4d0f7) into main (ca0018d) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #539   +/-   ##
=======================================
  Coverage   84.87%   84.87%           
=======================================
  Files           9        9           
  Lines         324      324           
  Branches      105      105           
=======================================
  Hits          275      275           
  Misses         46       46           
  Partials        3        3           

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[drwpow]

D‘oh! Thanks for fixing this. Also thanks for adding Node 15. I’ve been using it locally, but always good to have it in CI too.