Fixed the bashisms CI to only check files that exist

[koibtw]

Type of Change

• [x] Bug fix
• [x] Hotfix

Description

When a shell file is deleted or moved, this CI fails. This fixes it.

Checklist

• [x] My code adheres to the coding and style guidelines of the project.
• [x] I have performed a self-review of my own code.
• [x] My changes generate no errors/warnings/merge conflicts.