GitHub Script action not pinned to a full-length commit SHA

The `accessibility-scanner` workflow uses `actions/github-script@v8` without pinning it to a specific commit SHA. This violates security best practices and causes the pipeline to fail when the **Require actions to be pinned to a full-length commit SHA** setting is enabled.

#### **Steps to Reproduce**
1. Enable **Require actions to be pinned to a full-length commit SHA** in the repository settings.
2. Run the `accessibility-scanner` workflow.
3. Observe the failure caused by the unpinned `actions/github-script` action.

#### **Expected Behavior**
The workflow should run successfully with all actions pinned to full-length commit SHAs.

#### **Actual Behavior**
The workflow fails because `actions/github-script@v8` is not pinned to a commit SHA.

https://github.com/github/accessibility-scanner/blob/db51bb5d470a862cc027836ee1583ab9d5ae5b16/action.yml#L137