mgr/dashboard: fix flaky inventory e2e test

mgr/dashboard: fix flaky inventory e2e test

When `inventory.getTableCount('total').should('be.eq', totalDiskCount);`
this line is executed the table was not loaded properly and hence the
getTableCount returns 0 on the first try but on second try it passes
since the table is loaded. But in orch e2es the retries are set to 0. I
am not sure if it makes sense to set it to 1. Anyway I am adapting the
test a bit to expect the count to be equal to totalDiskCount so that the
test will wait a bit.

Fixes: https://tracker.ceph.com/issues/53353
Signed-off-by: Nizamudeen A <nia@redhat.com>