Skip tests of CORE::Dump on FreeBSD

Because on this OS this test writes to /var/log/messages

For: #18847

t/op/dump.t

@@ -68,6 +68,9 @@ plan(2);
 # chdirred to /tmp, a 'no' won't find the pragma. Hence the fiddling with
 # $SIG{__WARN__}.
 
+SKIP: {
+    my $reason = "GH 18847: excessive writes to /var/log/messages on FreeBSD";
+    skip $reason, 2 if $^O eq 'freebsd';
 fresh_perl_like(<<'PROG', qr/\AA(?!B\z)/, {}, "plain dump quits");
 BEGIN {$SIG {__WARN__} = sub {1;}}
 ++$|;
@@ -101,6 +104,8 @@ else {
 }
 PROG
 
+} # END SKIP block
+
 END {
   chdir $start if defined $start;
 }