Add 5 regression tests from PR #4476 (gnanam1990) to prevent re-introducing
the IGNORECASE bug that caused lowercase Python/TypeScript variable assignments
to be incorrectly redacted as secrets. The core fix landed in 6367e1c4.
Tests cover:
- Lowercase Python variable with 'token' in name
- Lowercase Python variable with 'api_key' in name
- TypeScript 'await' not treated as secret value
- TypeScript 'secret' variable assignment
- 'export' prefix preserved for uppercase env vars
Co-authored-by: gnanam1990 <gnanam1990@users.noreply.github.com>