"Not possible to fast-forward" when pull.ff=only and new commits on remote

After upgrade to 2.33.1, the behavior of `pull.ff=only` has changed in a way that breaks some workflows, notably the default used in VSCode.

Example (specific repo doesn't matter)

$ git clone git@github.com:kcarnold/util.git
...
$ cd util
$ echo "" > test
$ git add test
$ git commit -m "Test"
$ git -c pull.ff=only pull
fatal: Not possible to fast-forward, aborting.
$ git status
On branch master
Your branch is ahead of 'origin/master' by 1 commit.
  (use "git push" to publish your local commits)

Previously this pull succeeded without error, which was as expected because no merge was necessary. 

VS Code users have reported this problem because that editor has a "sync" option that seems to run something like `git pull && git push`.