chore: keep only the newest 5 dev prereleases

.github/workflows/dev-release.yml

@@ -167,11 +167,7 @@ jobs:
 
       # Kept rather than unbounded: the Worker reads the first page of releases to
       # resolve the channel, so enough prereleases would eventually push the real
-      # ones off it, and each build carries two assets.
-      #
-      # Twenty, not five. A pinned dev tag is how an external evaluator installs a
-      # specific build, and five is about a week of them -- short enough that the tag
-      # someone was given stops resolving while they are still using it.
+      # ones off it. Five leaves a few recent builds to roll back to.
       - name: Prune old dev prereleases
         if: steps.version.outputs.exists != 'true'
         env:
@@ -179,7 +175,7 @@ jobs:
         run: |
           set -euo pipefail
           gh api "repos/$GITHUB_REPOSITORY/releases?per_page=100" \
-              --jq 'map(select(.prerelease and (.tag_name | endswith("-dev")))) | .[20:] | .[].tag_name' \
+              --jq 'map(select(.prerelease and (.tag_name | endswith("-dev")))) | .[5:] | .[].tag_name' \
               > stale.txt
           while read -r tag; do
               [ -n "$tag" ] || continue