doc/rados/ops: edit health-checks.rst (2 of x)

doc/rados/ops: edit health-checks.rst (2 of x)

Edit docs/rados/operations/health-checks.rst (2 of x). PR#50674, the PR
that immediately precedes this PR in the series of PRs that line-edit
health-checks.rst, wrongly identified this series as having five
sections. This has been rectified by using the "2 of x" formulation.

Follows https://github.com/ceph/ceph/pull/50674

https://tracker.ceph.com/issues/58485

Signed-off-by: Zac Dover <zac.dover@proton.me>
(cherry picked from commit 0565f59698e9d00adf5a4667ac6e84e97d31b554)