zend_inheritance: Improve formatting of return-by-ref & in zend_get_function_declaration() (php#20104)

The space after `&` made it look like the `&` was not part of the signature,
possibly leading to confusion why the two signatures are incompatible without
carefully reading the message.

Author: TimWolla

Zend/tests/inheritance/argument_restriction_001.phpt

@@ -13,4 +13,4 @@ class Sub extends Base {
 }
 ?>
 --EXPECTF--
-Fatal error: Declaration of & Sub::test() must be compatible with & Base::test($foo, array $bar, $option = null, $extra = 'llllllllll...') in %s on line %d
+Fatal error: Declaration of &Sub::test() must be compatible with &Base::test($foo, array $bar, $option = null, $extra = 'llllllllll...') in %s on line %d

Zend/tests/objects/objects_005.phpt

@@ -19,4 +19,4 @@ class test3 extends test {
 
 ?>
 --EXPECTF--
-Fatal error: Declaration of test3::foo() must be compatible with & test::foo() in %s on line %d
+Fatal error: Declaration of test3::foo() must be compatible with &test::foo() in %s on line %d

Zend/tests/property_hooks/get_by_ref_implemented_by_val.phpt

@@ -15,4 +15,4 @@ class A implements I {
 
 ?>
 --EXPECTF--
-Fatal error: Declaration of A::$prop::get() must be compatible with & I::$prop::get() in %s on line %d
+Fatal error: Declaration of A::$prop::get() must be compatible with &I::$prop::get() in %s on line %d

Zend/zend_inheritance.c

@@ -916,7 +916,7 @@ static ZEND_COLD zend_string *zend_get_function_declaration(
 	smart_str str = {0};
 
 	if (fptr->op_array.fn_flags & ZEND_ACC_RETURN_REFERENCE) {
-		smart_str_appends(&str, "& ");
+		smart_str_appendc(&str, '&');
 	}
 
 	if (fptr->common.scope) {