release: use rare opt-out token that prose won't match

the previous guard string kept matching because i literally mentioned
it in my own commit messages when documenting the feature. switched
to a form with an equals sign that will never appear in ordinary
english.

.github/workflows/release.yml

@@ -9,10 +9,10 @@ name: release
 #      (amd64 + arm64) and attaches them plus checksums.txt to a fresh
 #      GitHub Release page
 #
-# Skip a release by putting [skip-release] anywhere in the commit
-# message (note the hyphen) — useful for docs-only or ci-only
-# commits. We use [skip-release] rather than [skip release] so that
-# commits that merely *mention* the phrase don't accidentally opt out.
+# Skip a release by putting [release=skip] anywhere in the commit
+# message — useful for docs-only or ci-only commits. We use a rare
+# equals-sign form so commits that merely *mention* the feature
+# ("make the release step optional") don't accidentally opt out.
 on:
   workflow_run:
     workflows: [ci]
@@ -33,7 +33,7 @@ jobs:
   release:
     # Only run when ci succeeded and we're on main, and when the head
     # commit doesn't opt out via [skip-release].
-    if: ${{ github.event.workflow_run.conclusion == 'success' && github.event.workflow_run.head_branch == 'main' && !contains(github.event.workflow_run.head_commit.message, '[skip-release]') }}
+    if: ${{ github.event.workflow_run.conclusion == 'success' && github.event.workflow_run.head_branch == 'main' && !contains(github.event.workflow_run.head_commit.message, '[release=skip]') }}
     runs-on: ubuntu-latest
     steps:
       - name: checkout