gdb: make typing strict in gdb/copyright.py

gdb: make typing strict in gdb/copyright.py

Add `pyright: strict` at the top of the file, then adjust the fallouts.
This annotation is understood by pyright, and thus any IDE using pyright
behind the scenes (VSCode and probably others).

I presume that any GDB developer running this script is using a recent
enough version of Python, so specify the type annotations using the
actual types when possible (e.g. `list[str]` instead of
`typing.List[str]`).  I believe this required Python 3.9.

Change-Id: I3698e28555e236a03126d4cd010dae4b5647ce48
Reviewed-By: Guinevere Larsen <guinevere@redhat.com>