github: add tentacle milestone

pull requests based on the tentacle branch aren't setting the milestone

Signed-off-by: Casey Bodley <[email protected]>
(cherry picked from commit 88cdbc2)

Author: cbodley

.github/milestone.yml

@@ -6,3 +6,4 @@ base-branch:
   - "(quincy)"
   - "(reef)"
   - "(squid)"
+  - "(tentacle)"

doc/dev/release-checklists.rst

@@ -133,7 +133,7 @@ After dev freeze
 - [ ] cherry-pick 8cf9ad62949516666ad0f2c0bb7726ef68e4d666 ("doc: add releases links to toc"). There will be trivial conflicts.
 - [ ] add redirect for new major release at `RTD <https://readthedocs.org/dashboard/ceph/redirects/>`_.
 - [x] add release name to redmine (using https://tracker.ceph.com/custom_fields/16/edit)
-- [ ] add release name to .github/milestone.yml for github actions to automatically add milestone to backports (this commit must be backported to the release branch)
+- [x] add release name to .github/milestone.yml for github actions to automatically add milestone to backports (this commit must be backported to the release branch)
 - [ ] add release branch to nightlies: qa/crontab/teuthology-cronjobs
 
 First release candidate