refactor: combine events.csv modifications to avoid conflicts

[hsolleder]

James suggested the following change to the events.csv modification pipeline

Currently, when events are confirmed, it opens a pull request in the git repo with changes to the events.csv file. It can be the case that many events are added simultaneously, leading to multiple pull requests. Merging the first pull request works fine but after that all the remaining pull requests are in conflict with the master and need to have conflicts resolved before they can be merged.

I would suggest that all edits to the events.csv file are on the same branch and pull request such that the dataset maintainer only needs to check and merge one pull request without any merge conflicts.