Bugfix: Fix order in TimeZone.p.getOffsetStringFor

This was an omission in #2519, a recently-merged normative change, that
Anba spotted after the fact. Possibly a rebase error.

Makes getOffsetStringFor consistent with getPlainDateTimeFor and
getInstantFor. The reference code was already correct here.

Closes: #2775

spec/timezone.html

@@ -141,8 +141,8 @@ <h1>Temporal.TimeZone.prototype.getOffsetStringFor ( _instant_ )</h1>
       <emu-alg>
         1. Let _timeZone_ be the *this* value.
         1. Perform ? RequireInternalSlot(_timeZone_, [[InitializedTemporalTimeZone]]).
-        1. Let _timeZoneRec_ be ? CreateTimeZoneMethodsRecord(_timeZone_, « ~get-offset-nanoseconds-for~ »).
         1. Set _instant_ to ? ToTemporalInstant(_instant_).
+        1. Let _timeZoneRec_ be ? CreateTimeZoneMethodsRecord(_timeZone_, « ~get-offset-nanoseconds-for~ »).
         1. Return ? GetOffsetStringFor(_timeZoneRec_, _instant_).
       </emu-alg>
     </emu-clause>