Shared _release-please.yml fails on label race after PR creation

[JacobPEvans]

Symptom

The shared `_release-please.yml` reusable workflow fails after successfully opening release PRs. Affects every consumer:

Repo	Failures (last 100 runs)
nix-home	30
ansible-proxmox-apps	21
terraform-proxmox	17
ansible-splunk	11
ansible-proxmox	12

Root cause

`googleapis/release-please-action@v5` opens the release PR successfully, then immediately tries to apply `autorelease: pending` labels via GraphQL. The PR's global node ID hasn't propagated yet, so GitHub returns:

```text
Validation Failed: Could not resolve to a node with the global id of 'PR_kwDO...'
```

The action exits non-zero even though the PR was created correctly. This is a race condition in the upstream action.

(Note: older failures from 2026-03 were a separate `GH_APP_PRIVATE_KEY` missing-secret bug — already fixed.)

Fix options (in order of preference)

1. Upgrade `googleapis/release-please-action` — check for a newer tag fixing the label-timing issue.
2. Tolerate the label failure — `continue-on-error: true` on the action step, gate downstream steps on `steps.release.outputs.pr` rather than job success. Least invasive, preserves labels when they do succeed.
3. `skip-labeling: true` — disables `autorelease: pending` entirely. Simplest, but breaks any tooling that reads the label.

Recommend trying #1, falling back to #2.

Affected files

• `.github/workflows/_release-please.yml` (this repo — single source of truth)
• Per-repo callers (no fix needed — identical 16-line shims)