fix: protected method in final class -> private is not a BC break

A method should only be considered "accessible" outside the class if:

* It is `public`
* It is `protected` and the class is NOT `final`

Previously, `protected` methods in `final` classes were incorrectly
considered to be accessible. This meant that changing one to `protected`
would incorrectly be reported as a BC break.

This commit fixes that logic.

Author: acoulton

src/DetectChanges/BCBreak/ClassBased/MethodRemoved.php

@@ -44,9 +44,8 @@ public function __invoke(ReflectionClass $fromClass, ReflectionClass $toClass):
     /** @return array<string, ReflectionMethod> */
     private function accessibleMethods(ReflectionClass $class): array
     {
-        $methods = Vec\filter($class->getMethods(), function (ReflectionMethod $method): bool {
-            return ($method->isPublic()
-                || $method->isProtected())
+        $methods = Vec\filter($class->getMethods(), function (ReflectionMethod $method) use ($class): bool {
+            return $this->isAccessibleMethod($method, $class)
                 && ! $this->isInternalDocComment($method->getDocComment());
         });
 
@@ -58,6 +57,15 @@ private function accessibleMethods(ReflectionClass $class): array
         );
     }
 
+    private function isAccessibleMethod(ReflectionMethod $method, ReflectionClass $class): bool
+    {
+        if ($method->isPublic()) {
+            return true;
+        }
+
+        return $method->isProtected() && ! $class->isFinal();
+    }
+
     private function isInternalDocComment(string|null $comment): bool
     {
         return $comment !== null