Fix crash in temp/let with parametarized hashes

Fixes RT#127291: https://rt.perl.org/Ticket/Display.html?id=127291

When we stash the hash for later restoration, we copy it into
a non-parametarized hash that stringifies the keys, causing a crash
when it's later restored into parametarized container.

Fix by stashing the hash into Mu/Mu parameterized hash that
leaves values untouched.

src/core/Rakudo/Internals.pm

@@ -194,7 +194,7 @@ my class Rakudo::Internals {
                   nqp::push(restore,my @ = cont),
                   nqp::if(
                     nqp::istype(cont,Hash),
-                    nqp::push(restore,my % = cont),
+                    nqp::push(restore,Hash.^parameterize(Mu,Mu).new: cont),
                     nqp::stmts(
                       nqp::pop(restore),  # lose the erroneously pushed value
                       X::Localizer::NoContainer.new(:$localizer).throw