Support loading builtin booleans

Since perl 5.36, PL_sv_yes/PL_sv_no will be preserved as booleans.
If we create them with newSVsv(), they are not readonly anymore and
will still roundtrip.

Also add a cleanup in t/file.t

LibYAML/perl_libyaml.c

@@ -549,7 +549,11 @@ load_scalar(perl_yaml_loader_t *loader)
                 scalar = sv_setref_iv(scalar, name, 1);
             }
             else {
+#ifdef PERL_HAVE_BOOLEANS
+                scalar = newSVsv(&PL_sv_yes);
+#else
                 scalar = &PL_sv_yes;
+#endif
             }
             if (anchor)
                 hv_store(loader->anchors, anchor, strlen(anchor), SvREFCNT_inc(scalar), 0);
@@ -567,7 +571,11 @@ load_scalar(perl_yaml_loader_t *loader)
                 scalar = sv_setref_iv(scalar, name, 0);
             }
             else {
+#ifdef PERL_HAVE_BOOLEANS
+                scalar = newSVsv(&PL_sv_no);
+#else
                 scalar = &PL_sv_no;
+#endif
             }
             if (anchor)
                 hv_store(loader->anchors, anchor, strlen(anchor), SvREFCNT_inc(scalar), 0);

t/boolean.t

@@ -1,7 +1,7 @@
 use FindBin '$Bin';
 use lib $Bin;
 use constant HAVE_BOOLEANS => ($^V ge v5.36);
-use TestYAMLTests tests => 5 + (HAVE_BOOLEANS ? 2 : 0);
+use TestYAMLTests tests => 5 + (HAVE_BOOLEANS ? 4 : 0);
 
 my $yaml = <<'...';
 ---
@@ -58,4 +58,8 @@ if( HAVE_BOOLEANS ) {
 'true': true
 ...
         'booleans loaded as core booleans';
+
+    eval { $hash->{a} = 'something else' };
+    is $@, '', "core boolean element in hash is not readonly";
+    is $hash->{a}, 'something else', "core boolean element is changed";
 }

t/file.t

@@ -31,3 +31,7 @@ YAML::XS::DumpFile($test_file, $t3, $t4);
 my ($t3_, $t4_) = LoadFile($test_file);
 
 is_deeply [$t3_, $t4_], [$t3, $t4], 'Unicode roundtrip ok';
+
+END {
+    rmtree('t/output');
+}