Improve Copyright Detection

[AyanSinhaMahapatra]

Tasks

• Reviewed contribution guidelines
• PR is descriptively titled 📑 and links the original issue above 🔗
• Tests pass -- look for a green checkbox ✔️ a few minutes after opening your PR
  Run tests locally to check for errors.
• Commits are in uniquely-named feature branch and has no merge conflicts 📁
• Updated documentation pages (if applicable)
• Updated CHANGELOG.rst (if applicable)

[pombredanne]

The Azure CI is flaky and randomly fails with:

E               ERROR: Unknown error:
E               Traceback (most recent call last):
E                 File "/home/vsts/work/1/s/src/scancode/interrupt.py", line 89, in interruptible
E                   create_signal(SIGALRM, handler)
E                 File "/opt/hostedtoolcache/Python/3.9.20/x64/lib/python3.9/signal.py", line 56, in signal
E                   handler = _signal.signal(_enum_to_int(signalnum), _enum_to_int(handler))
E               ValueError: signal only works in main thread of the main interpreter

This is an heisenbug only on Azure so I am going to merge anyway.