mediawiki.inspect: Fix doc index for inspect.grep()

mediawiki.inspect: Fix doc index for inspect.grep()

Because this was positioned linearly after the sub-object for
`mw.inspect.reports.*`, JSDuck was indexing this as part of that
object instead of the outer `mw.inspect.*` scope.

This could be fixed by adding `@member mw.inspect` on this method,
or by re-starting the `@class mw.inspect` scope, but really
this should've been declared closer to the rest of that class,
which naturally avoids the index issue.

Change-Id: Ib2c9dc861f7f062c05bc059643a1a676906d338f