[Bug]: pr-size-label fails when the runner proxy drops the GitHub API TLS connection

### Is there an existing issue for the same bug?

- [x] I searched open and closed matrixorigin/matrixone issues for pr-size-label, the exact TLS error, the GitHub API endpoint, and the self-hosted runner proxy; no matching issue was found. #4117 is the closed implementation subtask, not this runtime failure.

### Branch Name

agent/issue-27042-95f434d9 (PR #27070 against main)

### Commit ID

- PR head: 1b76b5bcfeed27e4b70d77615cc010fdfc382b70
- PR base: bdbd613fdece966769eb68481a3e58bfbc36b30c

### Other Environment Information

- Workflow: MatrixOne ALL CI
- Event: pull_request_target
- Run: https://github.com/matrixorigin/matrixone/actions/runs/31703445493
- Failed job: https://github.com/matrixorigin/matrixone/actions/runs/31703445493/job/94458009359
- Run attempt: 1
- Runner: arm64-mo-shanghai-4c8g-jj2z7-runner-4mlsk
- Proxy: http://proxy-service.proxy.svc.cluster.local:8001
- Shared action: matrixorigin/CI/actions/label-size-action@main, workflow revision 2f8b38b47335613a44dd8043d2c305fcec5adc72

### Actual Behavior

The pr-size-label job failed before it could read or classify PR #27070. Runner setup first failed to resolve the shared action download metadata, retried, and eventually loaded the action. The action then attempted to fetch the PR from GitHub's API and its TLS connection was dropped before establishment:

```text
Failed to resolve action download info. Error: An error occurred while sending the request.
Retrying in 21.357 seconds
...
The PR number of this job is: 27070
request to https://api.github.com/repos/matrixorigin/matrixone/pulls/27070 failed, reason: Client network socket disconnected before secure TLS connection was established
```

The job ended immediately after that network exception. No diff-size calculation or label mutation ran.

### Expected Behavior

A transient proxy/GitHub API connection failure should be retried with bounded backoff, or the runner/proxy path should reliably establish TLS. The PR size check should not fail permanently before evaluating the PR.

### Steps to Reproduce

1. Trigger MatrixOne ALL CI through a pull_request_target event on a MatrixOne PR.
2. Schedule Matrixone Utils CI / pr-size-label on the Shanghai self-hosted ARM64 runner behind proxy-service.proxy.svc.cluster.local:8001.
3. During action setup or the action's GET /repos/matrixorigin/matrixone/pulls/ call, reproduce a transient proxy/TLS disconnect.
4. Observe the action terminate without retrying the PR API request and the job conclude failure.

### Additional information

This failure is unrelated to PR #27070:

- the action never obtained the PR response and therefore never inspected the changed files or line count;
- the previous workflow for the same head completed pr-size-label successfully;
- the PR changes temporary-table clone handling and tests, not the shared label action, workflow, runner, proxy, or network stack;
- the same failed job log records an earlier action-download network error, independently corroborating runner/proxy instability.

The root-cause fix belongs in the runner/proxy reliability path or the shared label action's bounded retry behavior. This PR should not be changed to mask the infrastructure failure.