Try caching npm

[rchiodo]

Added cache for npm

Not sure it helps in the default case. The npm cache works but npm ci still stakes about the same amount of time. Maybe when the network is down it will prevent failures.

[codecov-io]

Codecov Report

Merging #8436 into master will decrease coverage by 0.32%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #8436      +/-   ##
==========================================
- Coverage   59.46%   59.14%   -0.33%     
==========================================
  Files         509      509              
  Lines       23390    23390              
  Branches     3779     3774       -5     
==========================================
- Hits        13909    13834      -75     
- Misses       8575     8650      +75     
  Partials      906      906

Impacted Files	Coverage Δ
src/client/testing/serviceRegistry.ts	48.64% <0%> (-46.85%)	⬇️
src/client/testing/codeLenses/main.ts	44.44% <0%> (-33.34%)	⬇️
...t/datascience/jupyter/jupyterDataRateLimitError.ts	66.66% <0%> (-33.34%)	⬇️
src/client/formatters/serviceRegistry.ts	75% <0%> (-25%)	⬇️
...ience/jupyter/jupyterDebuggerRemoteNotSupported.ts	75% <0%> (-25%)	⬇️
...cience/jupyter/jupyterDebuggerNotInstalledError.ts	60% <0%> (-20%)	⬇️
src/client/common/utils/icons.ts	83.33% <0%> (-16.67%)	⬇️
src/client/api.ts	78.57% <0%> (-14.29%)	⬇️
src/client/datascience/cellFactory.ts	57.69% <0%> (-12.83%)	⬇️
src/client/providers/providerUtilities.ts	83.33% <0%> (-5.56%)	⬇️
... and 2 more

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