T6755: Change default vyos mirror URL

[sever-sever]

Change Summary

Change default vyos mirror URL

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
• [x] Other (please describe): change default vyos mirror URL

Related Task(s)

• https://vyos.dev/T6755

Related PRs

https://github.com/vyos/vyos-1x/pull/4119

Component(s) name

Proposed changes

How to test

build iso image

[2024-10-02 07:27:08] lb source 
P: Source stage disabled, skipping
P: Build completed successfully
vyos_bld@2595ca2a1064:/vyos/work/tmp/vyos-build$

Checklist:

• [x] I have read the CONTRIBUTING document
• [x] I have linked this PR to one or more Phabricator Task(s)
• [x] My commit headlines contain a valid Task id
• [ ] My change requires a change to the documentation
• [ ] I have updated the documentation accordingly