GHSA-whvh-wf3x-g77j: 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 method directly (in addition to the separate check handling requests arriving through the HTTP API). The only runtime symptom was a RuntimeWarning: coroutine 'is_install_allowed' was never awaited.

This has security implications only for deployments that combine all of the following:

• a custom extension or downstream integration that imports PyPIExtensionManager and calls install() directly with a package name influenced by untrusted user input (the stock JupyterLab HTTP handler is not affected - it performs its own awaited allowlist check before calling install());
• an allowlist/blocklist configured with the intent of restricting which packages users can install;
• the (default) PyPI Extension Manager enabled; and
• kernels and terminals disabled or delegated to remote hosts, so that the custom extension’s install() call is the only available package-install vector (otherwise a user with kernel access can install packages directly regardless of this check)