Fix broken tests [#3535670]

Changes in Drupal Core broke the Feeds tests. Let's try to fix these. It looks like that the fix is already provided in #3444986: Empty file doesn't trigger clean() to delete all imported items by @codebymikey, so hopefully this can be resolved quickly.

Show commands

Start within a Git clone of the project using the version control instructions.

Add & fetch this issue fork’s repository

Or, if you do not have SSH keys set up on git.drupalcode.org:

Add & fetch this issue fork’s repository

3535670-fix-broken-tests changes, plain diff MR !217
Check out this branch for the first time

Check out existing branch, if you already have it locally