Cherry pick PR #9022: evergreen: Fix app_key retrieval when creating the pref store

[cobalt-github-releaser-bot]

Refer to the original PR: #9022

Ensure the app_key buffer is properly sized before and after
calling GetAppKey. Previously, std::string::reserve was used
which allocated capacity but did not change the string's logical
size. This leads to app_key being empty, causing the
prefs store file name to be incorrect.

Bug: 431862767

[cobalt-github-releaser-bot]

Caution

There were merge conflicts while cherry picking! Check out cherry-pick-main-9022 and fix the conflicts before proceeding. Check the log at https://github.com/youtube/cobalt/actions/runs/21893577578 for details.

[github-actions]

🤖 Gemini Suggested Commit Message

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evergreen: Fix app key retrieval in pref store

Previously, std::string::reserve was used to size the app_key buffer
before calling GetAppKey. This only allocated capacity and did not
change the string's logical size.

This issue caused app_key to be empty, leading to an incorrect
prefs store file name. This change uses std::string::resize to
ensure the buffer is properly sized before and after GetAppKey.

Bug: 431862767

---

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