The aforementioned change to `glob` surfaced a couple errors in the unit tests:

1. `test_glob_literal` was still testing the old behavior of non-existing paths
   being filtered out.
2. The post-process tests (`test_post_process_dry_run` and `test_post_process`)
   were now failing because post-process was being run without first collecting
   the media. This is a case where non-existing files were previously being
   filtered out silently but now cause an error. Running the collection stage
   before testing `post_process.