I work at a branch called blaBla.
I want to merge all new commits that have happened in master into one and then merge it into my branch.
You really don't want to do this. The only reasonable options for bringing changes from
master into a feature branch are:
Do a normal
git merge master without squashing its commits, so that Git can tell which commits your feature branch has in common with
master (otherwise you will likely suffer from numerous merge conflicts). Otherwise all the new changes in your squashed merge commit will seem like they were part of your new feature - not good.
git rebase master to replay your branch's changes on top of the latest from
master. This is my preferred workflow, as it structures your changes as "changes since
master" regardless of which
master you started with, but it comes with all the usual risks of rewriting history (e.g. communicate very carefully if you're going to
git push --force to a branch that others are depending on).