T6492: Check if all migrators have the executable bit set

[natali-rs1985]

Change Summary

Add check for migtration scripts to prevent build errors

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe): check for migration scripts

Related Task(s)

• https://vyos.dev/T6492

Related PR(s)

Component(s) name

makefile

Proposed changes

How to test

Smoketest result

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly

[github-actions]

👍
No issues in PR Title / Commit Title

[c-po]

@MergigyIo backport sagitta sagitta-stream circinus-stream equuleus equuleus-stream