Update Chapter 4: Automated COBOL Testing with GitHub Actions

[alim395]

Proposed changes

• New section in Chapter 4 on setting up automated testing with GitHub Actions

This change enhances the COBOL Programming Course by providing practical examples of modern development practices applied to mainframe programming.

Fixes # (No specific issue, but addresses the need for modern testing practices in the COBOL course)

Type of change

• New feature (change which adds functionality or features to the course)
• Documentation (change which modifies documentation related to the course)

Checklist:

• I have read the Contributing Guideline
• I have included a title and description for this PR
• I have DCO-signed all of my commits that are included in this PR
• I have tested it manually and there are no regressions found
• I have commented my code, particularly in hard-to-understand areas (if appropriate)
• I have made corresponding changes to the documentation (if appropriate)