* brotlicffi does not support python 2, so only include it as a build input of requests if requests is being built for python 3. otherwise, fall back to brotli. * requests 2.26 release notes specify that charset-normalizer is only for python 3, while chardet is only for python 2. correct build inputs to reflect this. (charset-normalizer does not build with python 2.) fixes #138584