fix: Use viewBox instead of viewbox in SVGs

[provokateurin]

Summary

The correct attribute name is viewBox and not viewbox: https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/viewBox

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)

[come-nc]

Should we have some kind of lint svg CI workflow?

[provokateurin]

/compile /

[nickvergessen]

Should we have some kind of lint svg CI workflow?

We should at least make sure this here is not breaking it again any time soon:
https://github.com/nextcloud/server/blob/master/build/image-optimization.sh#L89-L97

We can of course also run that script on CI and ensure an empty diff. But I would see it as a different task

[provokateurin]

We should at least make sure this here is not breaking it again any time soon

I ran it, it didn't modify the attribute 👍