This also updates the test filename in
`WP_Test_REST_Attachments_Controller::test_create_item_default_filename_title()`
to accurately match the actual file name.
Merges [39848] to the 4.7 branch.
git-svn-id: https://develop.svn.wordpress.org/branches/4.7@39849 602fd350-edb4-49c9-b593-d223f7449a82