gh-38176: fix and activate E305 in pyx files
this is adding the pycodestyle E305 check to pycodestyle-minimal in pyx
files
### :memo: Checklist
- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
URL: https://github.com/sagemath/sage/pull/38176
Reported by: Frédéric Chapoton
Reviewer(s): Frédéric Chapoton, Matthias Köppe
