Ignore PDF file during PR

[facusapienza21]

Currently, every-time someone does a PR to main there is a conflict in the main.pdf file that prevents the auto-merge and it cannot be solved directly from GitHub, but instead it needs to be solved from a local repository. This is rather annoying, specially considering that we are not interested in keeping control of the pdf file since this is automatically generated by the GitHub action at every new commit.

Is there any way to ignore this file during a PR? Maybe having a separate action that when a PR is open it sync the pdf separately? @fperez do you have any insight in how to do this? I really like the GH action for compiling the pdf, but it is disrupting the natural workflow of the PR with revision in the relevant files (.tex, .jl, etc).