PDF Docs builds are broken

[David Smith]

Since eaf7b563a5d3861026242fdb503a58f71acf17f6 the pdf build of the docs have been broken. See report on the ​forum.

I traced the commit which introduced this error by looking through the build logs on read the docs.

Pass - ​https://app.readthedocs.org/projects/django/builds/30151643/
Fail - ​https://app.readthedocs.org/projects/django/builds/30194393/

The error messages are along the lines of the following so seems to make sense that it's the identified commit that introduced the regression.

Missing input file '{internals/_images/contribution_process}

I suspect it is because a .pdf version of the image was not included as part that change.