fix(deps): update dependency kreait/firebase-php to v7.21.2

[renovate]

This PR contains the following updates:

Package	Change	Age	Confidence
kreait/firebase-php	7.21.1 -> 7.21.2

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Release Notes

kreait/firebase-php (kreait/firebase-php)

v7.21.2

Compare Source

Fixed

• Re-added the #[SensitiveParameter] attribute because, while it's not supported in PHP 8.1, it can still be used
  if placed in a standalone line above the variable or property.
• Re-added support for JSON files with any file extension
• With the introduction of Valinor, Service Account credentials were required to have more fields than necessary to
  work with the SDK, although it only needs the client email, private key, and project ID.

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