JupyterLab: Allowlist/blocklist check in `PyPIExtensionManager.install()` not enforced for direct callers (missing `await`)

The extension allowlist/blocklist check inside PyPIExtensionManager.install was not enforced due to a missing await. For purposes of JupyterLab this was a secondary defense-in-depth check: install was intended to enforce the allowlist/blocklist itself for any future uses and users calling this...