Previously, (presummably due to a typo) the `okToCacheOpaque` argument
of `DataGroup#cacheResponse()` was essentially never taken into account
(since opaque responses have a non-200 status code and thus `res.ok` is
always false).
This commit fixes the typo, which allows opaque responses to be cached
when `okToCacheOpaque` is true (i.e. in data groups using the
`freshness` strategy).
Fixes#30968
PR Close#30977
d7be38f84b