ci: credit changelog contributors inline and harden empty pr fromJSON (#1625)

Release publish runs leave steps.release.outputs.pr empty, so fromJSON crashed
even when the credit step was gated off. Credit external issue openers with an
inline thanks suffix on logical changelog bullets instead of a Thanks section.
Keep fatal API lookup logs status-only.

.github/workflows/release-please.yml

@@ -63,7 +63,9 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ steps.app-token.outputs.token }}
           GITHUB_REPOSITORY: ${{ github.repository }}
-          RELEASE_BRANCH: ${{ fromJSON(steps.release.outputs.pr).headBranchName }}
+          # fromJSON must tolerate empty pr: env is evaluated even when if: skips
+          # (publish runs leave pr unset). Empty object yields empty RELEASE_BRANCH.
+          RELEASE_BRANCH: ${{ fromJSON(steps.release.outputs.pr || '{}').headBranchName || '' }}
           MAINTAINER_LOGINS: ""
         run: |
           if [ -z "$RELEASE_BRANCH" ]; then