Users can suggest tags with spaces (but the suggestion can't be approved)

[Trilarion]

Describe the bug

See https://meta.codidact.com/posts/285658 A user suggested adding the tag "American English". Due to it having a space, a reviewer is unable to approve the edit.

To Reproduce

Suggest an edit with a tag with spaces.

Expected behavior

The server should refuse the suggested edit the same way it's refusing edits or posts.

The client should forbid tags with spaces already on the client side before one clicks on posting.