build: T6330: fix indentation for the version pinning file.

[fvlaicu]

Change Summary

Fix indentation for the version pinning file release.pref.chroot
This was broken with #550

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):

Related Task(s)

https://vyos.dev/T6330

Component(s) name

build

Proposed changes

Trivial change, as it fixes indentation.

How to test

Trivial change - doesn't require testing

Checklist:

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

[c-po]

Sorry, I did not see your PR on this one before merging #612.

Thank you for the fix!