Bug report

When O_TMPFILE is available:

1. tempfile.TemporaryFile(mode='wb') opens with O_RDWR instead of O_WRONLY, the opener callback ignores mode argument and always use _bin_openflags
2. _bin_openflags has both O_CREAT and O_EXCL set, the opener callback removes O_CREAT from flags but leave O_EXCL, this is an undefined behavior according to Linux open(2) manpage

Your environment

• CPython versions tested on: 3.10
• Operating system and architecture: Linux x86_64

Linked PRs

• gh-96531: tempfile.TemporaryFile should honour write-only mode #133235