Source Build License Scan fails during ScanCode pre_scan plugin initialization #5680

Description

The Source Build License Scan fails on release/10.0.4xx because ScanCode cannot initialize its pre_scan plugins. Scanning stops before license-baseline comparison; this is not evidence of a new unapproved license.

Evidence

Build 3116985, task log 356:

ValueError: did not find any 'pre_scan' hooks

LicenseScanTests.ScanForLicenses invokes scancode, which exits with code 1. The traceback goes through plugincode/pre_scan.py into pluggy.PluginManager.add_hookspecs (pluggy/_manager.py:366).