fix(ci): rename the cross-repo client — github-script already declares octokit

`actions/github-script` injects an `octokit` binding into the script scope, so
`const octokit = ...` aborts the run before any logic executes:

    SyntaxError: Identifier 'octokit' has already been declared

Caught on objectstack#4553's own merge — the first time the workflow ever ran.
The pre-merge `node --check` missed it because the test wrapper declared only
{github, context, core, require}; a wrapper that omits an injected identifier
cannot see a collision with it. The wrapper now carries the full injected set,
and the old spelling fails that check.

Author: claude

.github/workflows/cross-repo-issue-closer.yml

@@ -105,25 +105,25 @@ jobs:
 
             // A second client: `github` is bound to GITHUB_TOKEN, which has no
             // write access outside this repository.
-            const octokit = require('@actions/github').getOctokit(token);
+            const crossRepo = require('@actions/github').getOctokit(token);
 
             for (const [key, t] of targets) {
               try {
-                const { data: issue } = await octokit.rest.issues.get({
+                const { data: issue } = await crossRepo.rest.issues.get({
                   owner: t.owner, repo: t.repo, issue_number: t.number,
                 });
                 if (issue.state === 'closed') {
                   core.info(`${key} is already closed — skipping.`);
                   continue;
                 }
-                await octokit.rest.issues.createComment({
+                await crossRepo.rest.issues.createComment({
                   owner: t.owner, repo: t.repo, issue_number: t.number,
                   body:
                     `已由 ${thisRepo} 的 ${prUrl} 修复并合并。\n\n` +
                     `（跨仓库的关闭关键字不会自动生效，本条由 \`cross-repo-issue-closer\` 工作流代为收口。）\n\n` +
                     `---\n_Generated by [Claude Code](https://claude.ai/code)_`,
                 });
-                await octokit.rest.issues.update({
+                await crossRepo.rest.issues.update({
                   owner: t.owner, repo: t.repo, issue_number: t.number,
                   state: 'closed', state_reason: 'completed',
                 });