build: have Kokoro grab service account credentials from secret that will be rotated

[gcf-owl-bot[bot]]

• build: have Kokoro grab service account credentials from secret that will be rotated

Source-Link: https://github.com/googleapis/synthtool/commit/4a0230eb8dc497f36fd3839e6144982131f30a9d Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-nodejs:latest@sha256:f59941869d508c6825deeffce180579545fd528f359f549a80a18ec0458d7094

[codecov[bot]]

Codecov Report

Base: 68.87% // Head: 69.59% // Increases project coverage by +0.71% :tada:

Coverage data is based on head (10d7dcf) compared to base (12fea09). Patch has no changes to coverable lines.

:exclamation: Current head 10d7dcf differs from pull request most recent head cddcbcb. Consider uploading reports for the commit cddcbcb to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #861 +/- ## ========================================== + Coverage 68.87% 69.59% +0.71% ========================================== Files 7 5 -2 Lines 1253 1207 -46 Branches 58 58 ========================================== - Hits 863 840 -23 + Misses 389 366 -23 Partials 1 1 ``` | [Impacted Files](https://codecov.io/gh/googleapis/cloud-profiler-nodejs/pull/861?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=googleapis) | Coverage Δ | | |---|---|---| | [.mocharc.js](https://codecov.io/gh/googleapis/cloud-profiler-nodejs/pull/861?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=googleapis#diff-Lm1vY2hhcmMuanM=) | | | | [.prettierrc.js](https://codecov.io/gh/googleapis/cloud-profiler-nodejs/pull/861?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=googleapis#diff-LnByZXR0aWVycmMuanM=) | | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=googleapis). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=googleapis)

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