Editorial: Avoid hitting nonnull assertion for bestFormat

In a94a793 the desired behaviour when formatting Temporal objects was
accidentally applied to formatting Date objects. So

new Date().toLocaleDateString([],  { hour: "numeric" });

would result in bestFormat being null, and according to the type assertion
of the Intl.DateTimeFormat [[DateTimeFormat]] internal slot, that is not
possible.

Checking that _inherit_ = ~relevant~ here ensures the new behaviour is
only applied to Temporal objects, and the type assertion is not hit.

See: #3049

spec/intl.html

@@ -865,7 +865,7 @@ <h1>
               1. Set _formatOptions_.[[&lt;_prop_>]] to _value_.
               1. Set _needDefaults_ to *false*.
           1. If _needDefaults_ is *true*, then
-            1. If _anyPresent_ is *true*, return *null*.
+            1. If _anyPresent_ is *true* and _inherit_ is ~relevant~, return *null*.
             1. For each property name _prop_ of _defaultOptions_, do
               1. Set _formatOptions_.[[&lt;_prop_>]] to *"numeric"*.
             1. If _defaults_ is ~zoned-date-time~, then