RELEASING: remove pytest mailing list (#13472) (#13473)

It is no longer. (cherry picked from commit 80dfa2d) Co-authored-by: Ran Benita <ran@unusedvar.com>

Author: patchback[bot]

RELEASING.rst

@@ -168,7 +168,6 @@ Both automatic and manual processes described above follow the same steps from t
 
  To the following mailing lists:
 
- * pytest-dev@python.org (all releases)
  * python-announce-list@python.org (all releases)
  * testing-in-python@lists.idyll.org (only major/minor releases)