Fix repository listing for private GitHub profiles

[HarshMN2345]

GitHub returns HTTP 422 for repository searches scoped to an owner whose profile is private, even when the GitHub App installation can list that owner's repositories. searchRepositories() currently turns this into an empty result.

On search 422, verify that the requested owner matches the installation owner, then use the existing installation-repository listing and filtering path. Unknown owners still return no results, while authorization, rate-limit, and server errors retain their existing exceptions. Successful searches continue using GitHub search. The fallback uses the same local name filtering and pagination as restricted installations.

Validation: eight focused unit tests pass (16 assertions), including private profiles, case-insensitive owner matching, filtering across pages, unknown owners, normal search responses, and provider failures. Three cases fail against the original implementation. The complete unit suite passes: 96 tests, 393 assertions, one existing skip. Targeted PHPStan level 4, PHP syntax, formatting of added tests, and git diff --check pass. Tests use a provider fake and make no external requests.

Fixes appwrite/appwrite#7352.
Fixes appwrite/appwrite#8347.

[github-actions]

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