Call Set with Throw=false for [PutForwards] (#832)

This is what browsers actually implement. Tested by
web-platform-tests/wpt#21039.

Author: TimothyGu

index.bs

@@ -11667,7 +11667,7 @@ in which case they are exposed on every object that [=implements=] the interface
                     {{ECMAScript/TypeError}}.
                 1.  Let |forwardId| be the identifier argument of the [{{PutForwards}}] extended
                     attribute.
-                1.  Perform [=?=] <a abstract-op>Set</a>(|Q|, |forwardId|, |V|, <emu-val>true</emu-val>).
+                1.  Perform [=?=] <a abstract-op>Set</a>(|Q|, |forwardId|, |V|, <emu-val>false</emu-val>).
                 1.  Return <emu-val>undefined</emu-val>.
             1.  Set |idlObject| to the IDL [=interface type=] value that represents a reference
                 to |esValue|.