Fix checking if same-package protected module is imported in the inspected one (PY-32485)

It led to false negative when inspected reference resolves to an element in the same file

python/src/com/jetbrains/python/inspections/PyProtectedMemberInspection.java

@@ -82,9 +82,7 @@ public class PyProtectedMemberInspection extends PyInspection {
         return StreamEx
           .of(importSource.getReference(resolveContext).multiResolve(false))
           .map(ResolveResult::getElement)
-          .nonNull()
-          .map(PsiElement::getContainingFile)
-          .nonNull()
+          .select(PyFile.class)
           .map(PsiFile::getContainingDirectory)
           .nonNull()
           .map(PsiDirectory::getVirtualFile)

python/testSrc/com/jetbrains/python/inspections/PyProtectedMemberInspectionTest.java

@@ -94,6 +94,24 @@ public class PyProtectedMemberInspectionTest extends PyInspectionTestCase {
     doMultiFileTest("my_package/my_subpackage/module2.py");
   }
 
+  // PY-32485
+  public void testProtectedMemberOfSameFileClass() {
+    // created file should be considered as located inside a package so Python 3 is used here
+    runWithLanguageLevel(
+      LanguageLevel.PYTHON34,
+      () -> doTestByText("class A:\n" +
+                         "    def __init__(self, arg):\n" +
+                         "        self._arg = arg\n" +
+                         "\n" +
+                         "    def _f(self):\n" +
+                         "        return self._arg\n" +
+                         "\n" +
+                         "a = A(1)\n" +
+                         "print(<weak_warning descr=\"Access to a protected member _arg of a class\">a._arg</weak_warning>)\n" +
+                         "print(<weak_warning descr=\"Access to a protected member _f of a class\">a._f</weak_warning>())")
+    );
+  }
+
   @NotNull
   @Override
   protected Class<? extends PyInspection> getInspectionClass() {