GDScript: Fix return type of constructor call for extending class

modules/gdscript/tests/scripts/analyzer/errors/constructor_call_type.gd

@@ -0,0 +1,10 @@
+class A:
+	func _init():
+		pass
+
+class B extends A: pass
+class C extends A: pass
+
+func test():
+	var x := B.new()
+	print(x is C)

modules/gdscript/tests/scripts/analyzer/errors/constructor_call_type.out

@@ -0,0 +1,2 @@
+GDTEST_ANALYZER_ERROR
+Expression is of type "B" so it can't be of type "C".