MDL-73424 general: Internal methods must have same type as parent

Otherwise the error is thrown in PHP8.1

lib/dml/pgsql_native_moodle_recordset.php

@@ -133,10 +133,12 @@ class pgsql_native_moodle_recordset extends moodle_recordset {
         return $row;
     }
 
+    #[\ReturnTypeWillChange]
     public function current() {
         return (object)$this->current;
     }
 
+    #[\ReturnTypeWillChange]
     public function key() {
         // return first column value as key
         if (!$this->current) {
@@ -146,11 +148,11 @@ class pgsql_native_moodle_recordset extends moodle_recordset {
         return $key;
     }
 
-    public function next() {
+    public function next(): void {
         $this->current = $this->fetch_next();
     }
 
-    public function valid() {
+    public function valid(): bool {
         return !empty($this->current);
     }