Normative: Don't validate numeric timezone in ToRelativeTemporalObject

It was checking if parsing TimeZoneNumericUTCOffset from the provided
timeZoneName is *not* a list of errors, i.e. it matches the production.
If that's the case, it would try to validate and normalize the time zone
offset, which would both fail - these steps should apply to an IANA time
zone name instead, i.e. when parsing *does* produce a list of errors and
the string doesn't match TimeZoneNumericUTCOffset.

This mistake was introduced in 2a81fbc, the updated code now matches the
validation & normalization steps in ToTemporalZonedDateTime.

spec/abstractops.html

@@ -493,7 +493,7 @@ <h1>ToRelativeTemporalObject ( _options_ )</h1>
         1. Let _offsetString_ be _result_.[[TimeZoneOffsetString]].
         1. Let _timeZoneName_ be _result_.[[TimeZoneIANAName]].
         1. If _timeZoneName_ is not *undefined*, then
-          1. If ParseText(StringToCodePoints(_timeZoneName_), |TimeZoneNumericUTCOffset|) is not a List of errors, then
+          1. If ParseText(StringToCodePoints(_timeZoneName_), |TimeZoneNumericUTCOffset|) is a List of errors, then
             1. If ! IsValidTimeZoneName(_timeZoneName_) is *false*, throw a *RangeError* exception.
             1. Set _timeZoneName_ to ! CanonicalizeTimeZoneName(_timeZoneName_).
           1. Let _timeZone_ be ! CreateTemporalTimeZone(_timeZoneName_).