Fix/only allow svg when uploading

[darylldoyle]

Description of the Change

Updates the plugin to only add SVGs as an allowed type, when the sanitiser will be able to run on those files.

How to test the Change

Changelog Entry

Added - New feature
Changed - Existing functionality
Deprecated - Soon-to-be removed feature
Removed - Feature
Fixed - Bug fix
Security - Vulnerability
Developer - Non-functional update

Credits

Props @username, @username2, ...

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added Critical Flows, Test Cases, and/or End-to-End Tests to cover my change.
• All new and existing tests pass.

[github-actions]

@darylldoyle thanks for the PR! Could you please fill out the PR template with description, changelog, and credits information so that we can properly review and merge this?

[dkotter]

So this doesn't work for me, I always get the Sorry, you are not allowed to upload this file type error message.

I think what's happening is there's an earlier mime check that fires before the wp_handle_upload_prefilter filter and since we aren't adding the svg mime until that filter runs, things no longer work.

To test, I'm in the Media Library admin page, with the Grid View on. If I drag and drop an svg image, I get the above error.

[dkotter]

I was curious on how our E2E tests were passing here when I couldn't get things to work. Looking into that, the uploadMedia command we use goes to /wp-admin/media-new.php and uploads from there. If I go to that page directly, I can upload svgs just fine but as mentioned above, I can't upload svgs from the main Media Library screen, which is interesting

[darylldoyle]

Thanks for flagging @dkotter! I too could replicate on the media grid view. I've resolved this and added additional tests for that. I also had to allow uploads from a few additional contexts, because otherwise you could only upload SVGs from the media pages. We might want to add some additional tests for these, but I don't have time at the moment.