[tests] test-license.py exclusion fails on Windows

tests/test-license.py builds absolute directory strings with a hard-coded slash suffix. On Windows, glob returns backslash paths, so the intended contrib/linux-kernel/test/include exclusion does not match and the license test reports xxhash.h and unaligned.h as failures. Reproduced on the dev branch with Python 3.13; using os.sep for the suffix makes the same test pass while preserving POSIX behavior. The focused fix is in PR branch codex/fix-license-test-windows.