How to update local master and merge a feature branch in a shorter way

My workflow to merge my feature branch with upstream remote is:

git stash / commit # save current work on feature branch
git checkout master
git pull
git checkout feature
git merge master

It seems to me I'm doing one too many steps. Is there a shorter workflow to achieve this? I could perhaps run git fetch and merge with origin/master but then my local master would go out of date?

You're correct.
You can do

git commit
git fetch
git merge origin/master

git fetch will get the latest changes from origin onto the origin/master branch allowing you to merge it into your feature branch.

You don't need to update your "local master", or change to the master branch in order to update origin/master, which is the thing you actually want to keep up-to-date with. All you need is git fetch which pulls in changes from the remote.

Once you've pulled in changes, you can rebase onto origin/master to move the commits from your branch on top of whatever has come in from the remote. I typically use rebase -i for this, so I can review the commits I'm moving.

The full set of steps is:

git fetch
git stash
git rebase -i origin/master
git stash pop

Note that, as is always the case when rebasing, you should make sure you are the only person working on the branch. Otherwise you will create divergent branches and there will be problems when other people try to incorporate your changes.