backport php 8 support from upstream
https://github.com/swig/swig/pull/1978 via
https://src.fedoraproject.org/rpms/swig/c/62dded8bacb09398b03d1352820636182d2494ab

Index: Lib/php/php.swg
--- Lib/php/php.swg.orig
+++ Lib/php/php.swg
@@ -465,7 +465,10 @@
 %php_typecheck(double,SWIG_TYPECHECK_DOUBLE,IS_DOUBLE)
 %php_typecheck(char,SWIG_TYPECHECK_CHAR,IS_STRING)
 
-%typemap(typecheck,precedence=SWIG_TYPECHECK_STRING) char *, char *&, char []
+%typemap(typecheck,precedence=SWIG_TYPECHECK_STRING) char *, char *&
+ " $1 = (Z_TYPE($input) == IS_STRING || Z_TYPE($input) == IS_NULL); "
+
+%typemap(typecheck,precedence=SWIG_TYPECHECK_STRING) char []
  " $1 = (Z_TYPE($input) == IS_STRING); "
 
 %typecheck(SWIG_TYPECHECK_POINTER) SWIGTYPE
