Data-Dumper: fix quotekeys.t test count for non-XS testing

This is a follow-up to 5b50ddc, which
added 4 tests without adjusting the skip count.

Previously, testing without XS available resulted in:

    t/quotekeys.t ................. Dubious, test returned 255 (wstat 65280, 0xff00)
    Failed 4/18 subtests
            (less 5 skipped subtests: 9 okay)
    ...
    t/quotekeys.t               (Wstat: 65280 (exited 255) Tests: 14 Failed: 0)
      Non-zero exit status: 255
      Parse errors: Bad plan.  You planned 18 tests but ran 14.

Author: mauke

dist/Data-Dumper/t/quotekeys.t

@@ -20,7 +20,7 @@ my $is_ascii = ord("A") == 65;
 
 run_tests_for_quotekeys();
 SKIP: {
-    skip "XS version was unavailable, so we already ran with pure Perl", 5
+    skip "XS version was unavailable, so we already ran with pure Perl", 9
         if $Data::Dumper::Useperl;
     local $Data::Dumper::Useperl = 1;
     run_tests_for_quotekeys();