TestSetterAndGetter: Apply the stirng callback fix also to 'value_callback', 'setter_callback' and 'expect_callback'

Author: TiSiE

src/TestCase/TestSetterAndGetterTrait.php

@@ -298,7 +298,7 @@ private function setterAndGetterNormalizeSpec($spec, string $name, object $targe
                 case 'value_callback':
                 case 'setter_value_callback':
                 case 'expect_callback':
-                    if (is_string($value)) {
+                    if (is_string($value) && !is_callable($value)) {
                         $value = [$this, $value];
                     }