X_RELEASE_BRANCH_NAME
Means
scripts/release.ts was run on a release/* branch that is not a release/<major>.x maintenance line
Typical cause
release/* is the maintenance lines' namespace, and ci.yml and release-tag.yml run on release/[0-9]+.x. The 31.1.0 bump branch was release/31.1.0: CI ran on its push and v31.1.0 was tagged on the PR head, off main's history (#1054). Checked under --dry-run too; a detached HEAD names no branch and is never refused. A bump PR's branch is chore/release-<version>
Fix
git switch -c chore/release-<version> — the fix line names the version being bumped to; then rerun the bump there