#17452: ci: Grant write perms for Issues for formal-conformance.yml

This pull request makes a minor update to the GitHub Actions workflow configuration by adjusting permissions to ensure proper functionality. * Updated the `.github/workflows/formal-conformance.yml` workflow to explicitly add `issues: write` permission, which is required for the workflow to function correctly. That's it. <!-- greptile_comment --> <h3>Greptile Summary</h3> Adds `issues: write` permission to the `formal-conformance.yml` workflow. This is required because the "Comment on PR" step (line 110-131) calls `github.rest.issues.createComment()` via `actions/github-script`, which needs the `issues: write` scope under GitHub's REST API. Without this permission, the step would fail with a 403 when drift is detected. - Correct and minimal fix — the permission is necessary for the existing `createComment` call to succeed. - One minor style note: the inline comment could be more descriptive about *why* the permission is needed. <h3>Confidence Score: 5/5</h3> - This PR is safe to merge — it adds a single necessary permission to an existing workflow. - The change is a one-line addition of a required permission (`issues: write`) that the workflow already needs for its `createComment` API call. No new code paths, no security concerns beyond the intended permission grant, and the scope is minimal. - No files require special attention. _{Last reviewed commit: 707ccfd} <!-- greptile_other_comments_section --> _{(5/5) You can turn off certain types of comments like style [here](https://app.greptile.com/review/github)!} <!-- /greptile_comment -->