Add npm version ci check

[mtrezza]

Adds a CI check that requires package-lock.json to be generated with npm <7.

Building with npm 7 causes errors that are difficult to interpret.
The discussion in #1344 shows that without a clear error message, contributors and reviewers unnecessarily spend more time to trace the issue back to npm 7.

This is analogous to parse-community/parse-server#7333.

[codecov]

Codecov Report

Merging #1345 (f516dd9) into master (490c8c1) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head f516dd9 differs from pull request most recent head d546e07. Consider uploading reports for the commit d546e07 to get more accurate results

@@           Coverage Diff           @@
##           master    #1345   +/-   ##
=======================================
  Coverage   99.23%   99.23%           
=======================================
  Files          60       60           
  Lines        5919     5920    +1     
  Branches     1346     1346           
=======================================
+ Hits         5874     5875    +1     
  Misses         44       44           
  Partials        1        1           

Impacted Files	Coverage Δ
src/ParseError.js	100.00% <100.00%> (ø)

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