ci(commitlint): skip on promotion PRs (next → main) too

Symmetric to the existing main → next sync-PR skip. Promotion PRs
aggregate the full next history including merge commits + the one-time
bootstrap commit (`merge: bring main 1.0.43 promotion commit into
next`) that uses a non-CC type. Per-commit CC has already been enforced
on the way INTO next, so re-validating the aggregate is redundant +
hits these unavoidable historical commits.

.github/workflows/commitlint.yml

@@ -30,12 +30,17 @@ jobs:
   lint:
     name: Lint commit messages
     runs-on: ubuntu-latest
-    # Skip on automated `main → next` sync PRs (head_ref=main): the
-    # commit range includes the autogenerated `Merge pull request #N
-    # from …` titles from prior promotions, which intentionally don't
-    # follow Conventional Commits. Each individual contributor PR was
-    # already linted before landing on main.
-    if: github.head_ref != 'main'
+    # Skip on:
+    #   • Automated `main → next` sync PRs (head_ref=main) — the commit
+    #     range includes autogenerated `Merge pull request #N from …`
+    #     titles from prior promotions.
+    #   • Promotion PRs `next → main` (head_ref=next, base_ref=main) —
+    #     same reason on the other side: these aggregate the full next
+    #     history including merge commits and the occasional bootstrap
+    #     commit that pre-dated the strict CC convention.
+    # Each individual contributor PR was already linted before landing
+    # on next, so no CC coverage is lost.
+    if: github.head_ref != 'main' && !(github.head_ref == 'next' && github.base_ref == 'main')
     steps:
       - uses: actions/checkout@v6
         with: