Fixed deprecation notices on PHP 8.1

src/Record/Iterator/Recursive_Record_Iterator.php

@@ -67,10 +67,10 @@ class Recursive_Record_Iterator extends \ArrayIterator implements \RecursiveIter
 	}
 
 	/**
-	 * @return static
+	 * This should be `static` for possible subclassing, but problems hinting that for PHP <8, also don't subclass this.
 	 */
-	public function getChildren() {
+	public function getChildren(): self {
 
-		return new static( $this->children );
+		return new self( $this->children );
 	}
 }

src/Record/Iterator/Timeline_Iterator.php

@@ -60,12 +60,14 @@ class Timeline_Iterator implements \Iterator {
 	}
 
 	/**
+	 * Key is unused and is only type hinted to possible `int` for PHP 8.1 `mixed` type compatibility.
+	 *
 	 * @codeCoverageIgnore
 	 *
-	 * @return void
+	 * @return null
 	 */
-	public function key(): void {
-
+	public function key(): ?int {
+		return null;
 	}
 
 	/**