ci: remove stabilityDays from renovate config

Removes `stabilityDays` (since renamed to `minimumReleaseAge`[0]) This
was holding PRs back for 3 days after the dep update was released. We
want these PRs basically ASAP and can tolerate subsequent point releases
if there are post-release issues that cause the upstream to cut
follow-ups.

[0]: https://docs.renovatebot.com/configuration-options/#minimumreleaseage

.github/renovate.json

@@ -11,7 +11,6 @@
   },
   "prCreation": "not-pending",
   "rangeStrategy": "update-lockfile",
-  "stabilityDays": 3,
   "github-actions": {
     "fileMatch": [
       "^ci\\/.*/[^/]+\\.ya?ml$"