Pass an absolutified path to CWD

Fixes a weird spectest failure in t/spec/S12-meta/exporthow.t
===SORRY!===
Type check failed in binding to parameter '$CWD'; expected Str but got IO::Path (IO::Path.new("/Users/ugexe/re...)

src/core/Distribution.pm6

@@ -78,7 +78,7 @@ role Distribution {
 role Distribution::Locally does Distribution {
     has IO::Path $.prefix;
     method content($address) {
-        my $handle = IO::Handle.new: path => IO::Path.new($address, :CWD($!prefix // $*CWD));
+        my $handle = IO::Handle.new: path => IO::Path.new($address, :CWD($!prefix.absolute // $*CWD.absolute));
         $handle // $handle.throw;
     }
 }