refactor: Update get_github_installation_ids to use httpx

[tofarr]

This PR updates the get_github_installation_ids function to use httpx instead of requests with call_sync_from_async. This change makes the code more consistent with other functions in the file and more efficient by using native async HTTP requests.

Changes:

• Replace requests with httpx.AsyncClient()
• Use async context manager for better resource management
• Update error handling to use httpx.HTTPError
• Remove explicit response.close() as it is handled by the context manager
• Make the code pattern consistent with other functions in the file

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To run this PR locally, use the following command:

docker run -it --rm   -p 3000:3000   -v /var/run/docker.sock:/var/run/docker.sock   --add-host host.docker.internal:host-gateway   -e SANDBOX_RUNTIME_CONTAINER_IMAGE=docker.all-hands.dev/all-hands-ai/runtime:0e13a48-nikolaik   --name openhands-app-0e13a48   docker.all-hands.dev/all-hands-ai/openhands:0e13a48