This pull request updates GitHub Actions workflow files to explicitly
set permissions for certain actions. (fixing the permissions issues)
**Workflow permissions updates:**
* Added explicit `issues: write` permission to the `assign.yml` workflow
to ensure it can modify issues as needed.
* Set `contents: write`, `actions: write`, and `checks: write`
permissions in the `build_all.yml` workflow to allow the workflow to
interact with repository contents, manage actions, and update checks.
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