Add `jest-mock` to dependencies (#7800)
Add `jest-mock` to dependencies (#7800)

It's being used by the chat export test, but is not listed as a dependency.

If we rely on it, we should rely on it.
matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk