ci: waive the PR-body template check for bot-authored PRs

[ion-alpha-dev]

What

Waives the "PR body follows template" check for bot-authored pull requests. The pr-body job still runs, so the check reports a real success status, but its enforcement step exits early when the event payload's author type is Bot. Human pull requests are held to the ## What / ## Why / ## How to verify template exactly as before.

Why

The template gate ran on every pull request, dependabot's included. Dependabot writes its own changelog-shaped body (release notes, commit ranges) that carries none of the required sections, so the check failed and the CI success rollup went red on every dependency bump. The only way to green one was to hand-edit the bot's body to prepend the template and force a re-run, since an edit is not a CI trigger. That is a manual workaround repeated on every bump, not a fix. The template is a rule for humans; a bot's body is not ours to rewrite.

Keeping the job running rather than skipping it means the check still reports a status, so the ci-success aggregator and branch protection are unaffected. Reading the author type from the payload covers dependabot and any other forge bot without hardcoding a login.

How to verify

# A human PR with a body missing a section still fails:
BODY="## What only" AUTHOR_TYPE="User" bash -c '
  missing=0
  for s in "## What" "## Why" "## How to verify"; do case "$BODY" in *"$s"*) ;; *) missing=1;; esac; done
  [ "$missing" -eq 0 ]'; echo "human exit: $?"   # non-zero

# A bot PR is waived regardless of body:
AUTHOR_TYPE="Bot" bash -c '[ "$AUTHOR_TYPE" = "Bot" ] && exit 0'; echo "bot exit: $?"   # 0

On this PR (human-authored) the check runs and passes because the body carries all three sections. The next dependabot PR, once rebased onto this change, reports the check green without a hand-edited body.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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