fix(test): avoid panic of SetStreamingManager() on sealed BaseApp (backport #24109)

[mergify]

this change should have been included in a9e7d5b

Description

Closes: #XXXX

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Summary by CodeRabbit

This release includes internal improvements that enhance our system’s maintainability and reliability. Although these changes do not affect application functionality, they streamline our internal testing setup for long-term quality improvements.

• Refactor
  • Improved the modularity of internal test initialization for a cleaner and more maintainable setup.

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This is an automatic backport of pull request #24109 done by [Mergify](https://mergify.com).