ci: remove python-updates from development branches

The python-updates branch is not a "development" branch in the sense of
ci/README.md's classification. That's because it allows force pushes.
When rewrites are possible, cherry-picking from this branch should not
be allowed, because the commit references will potentially end up out of
sync.

These kind of branches are now termed "Work-in-Progress" branches. Up
until recently these branches didn't work well for Pull Requests
targeting them, because Eval wouldn't run on them with a push event and
thus, Eval in the PR couldn't succeed either. That's now fixed, PRs
towards *any* WIP branch should work correctly.

(cherry picked from commit 55b046451c)

.github/workflows/push.yml

@@ -13,7 +13,6 @@ on:
       - release-*
       - staging-*
       - haskell-updates
-      - python-updates
 
 permissions: {}