PY-24637 Use non-resolvable built-in constants check for doctest and Jupyter references

Since the switch to the builtins from Typeshed we no longer have
the definitions for True, False, None for PY2. We have to ignore these
references via null highlighting severity as we do in the base method
for PyReferenceImpl.

python/ipnb/src/org/jetbrains/plugins/ipnb/psi/IpnbPyReference.java

@@ -25,7 +25,8 @@ public class IpnbPyReference extends PyReferenceImpl {
 
   @Override
   public HighlightSeverity getUnresolvedHighlightSeverity(TypeEvalContext context) {
-    return HighlightSeverity.WARNING;
+    final HighlightSeverity severity = super.getUnresolvedHighlightSeverity(context);
+    return severity != null ? HighlightSeverity.WARNING : null;
   }
 
   @NotNull

python/src/com/jetbrains/python/documentation/doctest/PyDocReference.java

@@ -51,7 +51,8 @@ public class PyDocReference extends PyReferenceImpl {
 
   @Override
   public HighlightSeverity getUnresolvedHighlightSeverity(TypeEvalContext context) {
-    return HighlightSeverity.WARNING;
+    final HighlightSeverity severity = super.getUnresolvedHighlightSeverity(context);
+    return severity != null ? HighlightSeverity.WARNING : null;
   }
 
   @NotNull

python/testData/inspections/PyUnresolvedReferencesInspection/py2TrueInDocTest.py

@@ -0,0 +1,5 @@
+def func(x, y):
+    """
+    >>> func(True, <warning descr="Unresolved reference 'True2'">True2</warning>)
+    """
+    return True, <error descr="Unresolved reference 'True2'">True2</error>

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

@@ -637,6 +637,11 @@ public class PyUnresolvedReferencesInspectionTest extends PyInspectionTestCase {
     doMultiFileTest();
   }
 
+  // PY-24637
+  public void testPy2TrueInDocTest() {
+    doTest();
+  }
+
   @NotNull
   @Override
   protected Class<? extends PyInspection> getInspectionClass() {