fix: scope group share child permission updates to usergroup

[kristian-zendato]

Summary

Restrict the group-share child update in DefaultShareProvider::update() so only TYPE_USERGROUP rows get new permissions/attributes. Public links that reuse parent for display are no longer escalated when the group share is edited.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI

[susnux]

@kristian-zendato can you please check this CI error? It seems to be related to your changes:

build/integration/sharing_features/sharing-v1-part3.feature:581 (on line 606)

[susnux]

/backport to stable35

[susnux]

/backport to stable33

[susnux]

/backport to stable34

[susnux]

/backport to stable32

[susnux]

/backport to stable31

[susnux]

/backport to stable30

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