Tests: Promote if.py to passing_tests

It generates IR, compiles, and now passes the kernel verifier, so it is no
longer a failing test. It sat in failing_tests/ with no test_config.toml entry,
which meant the framework already required it to pass at every level -- the
directory was merely misleading.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: r41k0u