repository: avoid leaking `fsmonitor` data

repository: avoid leaking `fsmonitor` data

The `fsmonitor` repo-setting data is allocated lazily. It needs to be
released in `repo_clear()` along the rest of the allocated data in
`repository`.

This is needed because the next commit will merge v2.39.4, which will
add a `git checkout --recurse-modules` call (which would leak memory
without this here fix) to an otherwise leak-free test script.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>