Fix Jira issues #ROOT-8722 and ROOT-8723

Add a few tests like "if (obj->IsA() != TClass::Class())" to prevent casting a TClass object to its class type.
For example: if (obj->InheritsFrom("TDirectory")) returns true in the case of obj being a TClass (of a TDirectory class); then, calling ((TDirectory *)obj)->GetListOfKeys() fails (crash or random behavior)