fix: call addSharedMetadataHeaders even when token has not expired

[hideto0710]

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Fixes #1114 🦕

---

npm test -- -g "getRequestHeaders should populate x-goog-user-project"

before

  refresh
    ✓ getRequestHeaders should populate x-goog-user-project header if quota_project_id present
    1) getRequestHeaders should populate x-goog-user-project header if quota_project_id present and token has not expired


  1 passing (43ms)
  1 failing

  1) refresh
       getRequestHeaders should populate x-goog-user-project header if quota_project_id present and token has not expired:
     AssertionError [ERR_ASSERTION]: Expected values to be strictly equal:
+ actual - expected

+ undefined
- 'my-quota-project'

after

  refresh
    ✓ getRequestHeaders should populate x-goog-user-project header if quota_project_id present
    ✓ getRequestHeaders should populate x-goog-user-project header if quota_project_id present and token has not expired

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[codecov]

Codecov Report

Merging #1116 (2b4714e) into master (8786d15) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1116   +/-   ##
=======================================
  Coverage   91.65%   91.65%           
=======================================
  Files          21       21           
  Lines        4157     4157           
  Branches      464      430   -34     
=======================================
  Hits         3810     3810           
  Misses        347      347           

Impacted Files	Coverage Δ
src/auth/oauth2client.ts	96.00% <100.00%> (ø)

---

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[hideto0710]

@googlebot I signed it!

[bcoe]

@hideto0710 good catch 👍 (CC: @sofisl). If I'm following correctly, the quota project was properly populated up until the token refreshed?

I understand, the problem was specifically when grabbing headers and happened prior to expiry 👍

[bcoe]

mind adding the additional test? thank you very much for the contribution 🎉

[bcoe]

I think we should also add a test that makes sure you get the appropriate header populated after the expiry?

(sorry for the slow review, we'll work on getting this out the door quickly.).

[bcoe]

@hideto0710 thank you very much for the contribution 👍