fix(scripts): use RuntimeError instead of bare string in demangle.py

[AmSach]

scripts/demangle.py line 111 contains raise "error" which is Python 2 syntax and does not work in Python 3. Under Python 3, this raises a confusing TypeError: exceptions must derive from BaseException instead of the intended runtime error.

Before:

if next(c_iter) != 'g':
    raise "error"

After:

if next(c_iter) != 'g':
    raise RuntimeError("error")

This is a minimal, single-line fix that preserves the existing error semantics. The other raise statements in the file (e.g. raise Truncated(), raise Exception(...)) are already Python 3 compatible. — Sent via @AmSach bot