Checks that the same videos are not listed multiple times in a project's config.yaml file.

If the same video was listed multiple times in the project's config.yaml file (e.g. under /data/videos/openfield.mov and /dlc-project-2024-04-14/videos/openfield.mov), then the labeled data for the video from /dlc-project-2024-04-14/labeled-data/openfield) would be added multiple times to the training-data dataframe.

If the same video name is present multiple times, a warning is printed and it is only kept once.