fix: cache GCE credentials

[JustinBeckwith]

No description provided.

[codecov-io]

Codecov Report

Merging #286 into master will decrease coverage by 0.1%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #286      +/-   ##
==========================================
- Coverage   92.31%   92.21%   -0.11%     
==========================================
  Files          13       13              
  Lines         833      835       +2     
  Branches      179      178       -1     
==========================================
+ Hits          769      770       +1     
- Misses         64       65       +1

Impacted Files	Coverage Δ
src/auth/googleauth.ts	85.84% <100%> (-0.34%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 12feb2c...65ef580. Read the comment docs.