Clarify backport instructions further (#28908)

.github/pull_request_template.md

@@ -2,9 +2,8 @@
 What does this PR do?
 
 ### TODO only if you're a HashiCorp employee
-- [ ] **Backport Labels:** If this PR is in the ENT repo and needs to be backported, backport  
-  to N, N-1, and N-2, using the `backport/ent/x.x.x+ent` labels. If this PR is in the CE repo, you should only backport to N, using the `backport/x.x.x` label, not the enterprise labels.
-    - [ ] If this fixes a critical security vulnerability or [severity 1](https://www.hashicorp.com/customer-success/enterprise-support) bug, it will also need to be backported to the current [LTS versions](https://developer.hashicorp.com/vault/docs/enterprise/lts#why-is-there-a-risk-to-updating-to-a-non-lts-vault-enterprise-version) of Vault. To ensure this, use **all** available enterprise labels.
+- [ ] **Backport Labels:** If this fix needs to be backported, use the appropriate `backport/` label that matches the desired release branch. Note that in the CE repo, the latest release branch will look like `backport/x.x.x`, but older release branches will be `backport/ent/x.x.x+ent`.
+    - [ ] **LTS**: If this fixes a critical security vulnerability or [severity 1](https://www.hashicorp.com/customer-success/enterprise-support) bug, it will also need to be backported to the current [LTS versions](https://developer.hashicorp.com/vault/docs/enterprise/lts#why-is-there-a-risk-to-updating-to-a-non-lts-vault-enterprise-version) of Vault. To ensure this, use **all** available enterprise labels.
 - [ ] **ENT Breakage:** If this PR either 1) removes a public function OR 2) changes the signature
   of a public function, even if that change is in a CE file, _double check_ that
   applying the patch for this PR to the ENT repo and running tests doesn't