The main CI is happening in the ci.yml, this is where the tests are run.
There is a separate workflow called proof-params-generate.yml, that pre-generates the Groth16 parameter files needed for testing. Those parameters are stored as GitHub Artifacts, which are then downloaded by any workflow that needs them. Those artifacts are available for 90 days. Hence this job runs every two months to regenerate them, but also to have enough time in case something breaks.
The proof-params-download Action is a helper for downloading the pre-generated Groth16 parameters.