[lint] Fix variables shadowing python builtins in gen-ninja-deps.py

Summary: Shadowing builtins can lead to unexpected behavior. Continuing work from D13740

Test Plan:

ninja generate_univalue_escapes_h
flake8 cmake/utils/gen-ninja-deps.py  # empty

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D13747