SWIG_Python_str_AsChar removal in SWIG 4.2.0

The replacement, SWIG_PyUnicode_AsUTF8AndSize, has different memory
management requirements.

Submitted upstream: <https://github.com/NLnetLabs/ldns/pull/232>

diff -ur ldns-1.8.3.orig/ldns-1.8.3/contrib/python/ldns_rdf.i ldns-1.8.3/ldns-1.8.3/contrib/python/ldns_rdf.i
--- ldns-1.8.3.orig/ldns-1.8.3/contrib/python/ldns_rdf.i	2022-08-15 12:38:22.000000000 +0200
+++ ldns-1.8.3/ldns-1.8.3/contrib/python/ldns_rdf.i	2024-01-26 11:28:52.983540469 +0100
@@ -56,7 +56,11 @@
  */
 %typemap(arginit, noblock=1) const ldns_rdf *
 {
+#if SWIG_VERSION >= 0x040200
+  PyObject *$1_bytes = NULL;
+#else
   char *$1_str = NULL;
+#endif
 }
 
 /*
@@ -66,11 +70,17 @@
 %typemap(in, noblock=1) const ldns_rdf * (void* argp, $1_ltype tmp = 0, int res)
 {
   if (Python_str_Check($input)) {
+    const char *argstr;
+#if SWIG_VERSION >= 0x040200
+    argstr = SWIG_PyUnicode_AsUTF8AndSize($input, NULL, &$1_bytes);
+#else
     $1_str = SWIG_Python_str_AsChar($input);
-    if ($1_str == NULL) {
+    argstr = $1_str;
+#endif
+    if (argstr == NULL) {
       %argument_fail(SWIG_TypeError, "char *", $symname, $argnum);
     }
-    tmp = ldns_dname_new_frm_str($1_str);
+    tmp = ldns_dname_new_frm_str(argstr);
     if (tmp == NULL) {
       %argument_fail(SWIG_TypeError, "char *", $symname, $argnum);
     }
@@ -90,10 +100,17 @@
  */
 %typemap(freearg, noblock=1) const ldns_rdf *
 {
+#if SWIG_VERSION >= 0x040200
+  if ($1_bytes != NULL) {
+    /* Is not NULL only when a conversion form string occurred. */
+    Py_XDECREF($1_bytes);
+  }
+#else
   if ($1_str != NULL) {
     /* Is not NULL only when a conversion form string occurred. */
     SWIG_Python_str_DelForPy3($1_str); /* Is a empty macro for Python < 3. */
   }
+#endif
 }
 
 %nodefaultctor ldns_struct_rdf; /* No default constructor. */