Make sure BagHash/MixHash.push-all push proxies as well

Because PositionalBindFailover uses .push-all internally to generate its
cache of values, we need to pass proxies in there to make %bh <<+=>> 3 work

Spotted while writing exhaustive infix metaop tests.

src/core/BagHash.pm6

@@ -212,12 +212,10 @@ my class BagHash does Baggy {
             )
         }
 
-        # same as Baggy.values
         method push-all($target --> IterationEnd) {
             nqp::while(  # doesn't sink
               $!iter,
-              $target.push(nqp::getattr(
-                nqp::iterval(nqp::shift($!iter)),Pair,'$!value'))
+              $target.push(proxy(nqp::shift($!iter),$!hash))
             )
         }
     }

src/core/MixHash.pm6

@@ -193,12 +193,10 @@ my class MixHash does Mixy {
             )
         }
 
-        # same as Baggy.values
         method push-all($target --> IterationEnd) {
             nqp::while(  # doesn't sink
               $!iter,
-              $target.push(nqp::getattr(
-                nqp::iterval(nqp::shift($!iter)),Pair,'$!value'))
+              $target.push(proxy(nqp::shift($!iter),$!hash))
             )
         }
     }