fix: follow up fix service account credentials createScopedRequired

[arithmetic1728]

Address #601 (comment)

[codecov]

Codecov Report

Merging #605 (e5a3764) into master (3d066ee) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             master     #605   +/-   ##
=========================================
  Coverage     83.59%   83.59%           
- Complexity      602      604    +2     
=========================================
  Files            42       42           
  Lines          2712     2712           
  Branches        289      289           
=========================================
  Hits           2267     2267           
  Misses          303      303           
  Partials        142      142           

Impacted Files	Coverage Δ	Complexity Δ
.../google/auth/oauth2/ServiceAccountCredentials.java	83.50% <100.00%> (ø)	67.00 <3.00> (+2.00)

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