[io grant] Test $*TMPDIR can be temped

Rakudo fix: rakudo/rakudo@b62d1a768a

Author: zoffixznet

S16-io/tmpdir.t

@@ -3,11 +3,21 @@ use Test;
 
 # L<S16/IO/$*TMPDIR>
 
-plan 7;
+plan 9;
 
 isa-ok $*TMPDIR, IO::Path;
 lives-ok { $*TMPDIR.perl }, '$*TMPDIR.perl works';
 lives-ok { $*TMPDIR.gist }, '$*TMPDIR.gist works';
 
 isa-ok .tmpdir, IO::Path, "{.^name}.tmpdir returns IO::Path"
     for IO::Spec::Unix, IO::Spec::Win32, IO::Spec::Cygwin, IO::Spec::QNX;
+
+{
+    my $before = $*TMPDIR;
+    {
+        temp $*TMPDIR = '/foo'.IO;
+        is-deeply $*TMPDIR, '/foo'.IO, 'was able to `temp` $*TMPDIR';
+    }
+    is-deeply $*TMPDIR, $before,
+        '`temp`ed $*TMPDIR got restored to previous value';
+}