fix(dav): Public WebDAV endpoint should allow GET requests

[susnux]

• Resolves: [Bug]: Viewing media files via a share link doesn't work anymore #48475

Summary

GET should be allowed even without Ajax header to allow downloading files, or show files in the viewer. All other requests could be guarded, but this should not.

I think this was copy-paste from the v1 implementation, but that did not provide GET support, so for the old endpoint it made sense. But now with GET support we need to allow browsers to access the files without custom headers.

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)

[susnux]

/backport to stable30

[susnux]

/backport to stable29

[provokateurin]

Makes sense 👍

[backportbot]

The backport to stable29 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable29
git pull origin stable29

# Create the new backport branch
git checkout -b backport/48628/stable29

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick bbc5d32c

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/48628/stable29

Error: No changes found in backport branch

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Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.