fix(infra): fix trailing comma regex in profile generation script (#35333)

The trailing comma regex in the profile generation script consumed the
closing `}` as part of its match, preventing nested closing braces from
getting their own trailing comma. This caused `ruff format` failures on
every generated `_profiles.py` file.

Switches to a lookahead (`(?=...)`) so the closing bracket is asserted
but not consumed, allowing each nesting level to independently receive
its trailing comma.

Fixes #35332.