browser: fix sharing sidebar for files that were shared with me read-only

[alexanderdd]

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Steps to reproduce

1. userA shares an e2ee folder with userB as read-only, at least one file inside
2. userB opens the folder, and on a file, clicks on the sharing button or opens sidebar via details - sees the sharing tab in the right sidebar
3. none of the provided options in the sharing sidebar work (share internally, share externally via link), this is probably intentional

expected

only show options that work

versions

Nextcloud: 33.0.5

e2ee app: 2.1.1