Fix version's test scripts' $Verbose flag

Fix version's test scripts' $Verbose flag

The four scripts that use it should declare it a package variable, not a
lexical, otherwise the typeglob used in coretests.pm won't affect it.
Also, we want to set $Verbose to 0, not to $0, if $ENV{PERL_CORE} is set.

These customizations are being pushed upstream in CPAN RT#87513.