git move folder only by case sensitive name change

Question

I have a folder in git (on FS) called

fooBar

however, in git it is registered twice:

foobar and fooBar

so a How do I commit case-sensitive only filename changes in Git?

git mv -f foobar fooBar

fails with:

fatal: Umbenennung von 'foobar' fehlgeschlagen: Invalid argument

How can I synchronise it again i.e. only have a single reference to the FS object with name fooBar?