Add Missing "override" to EntitlementKeySession::Type()

(This is a merge of http://go/wvgerrit/73803)

While playing around with compiler settings, I found that
EntitlementKeySession::Type() is missing the `override` keyword.

Bug: 127498046
Test: CE CDM Build
Test: Android Build
Change-Id: I5a18dbbd425b0a493575a34b9f5f77b2d7c8f10d

libwvdrmengine/cdm/core/include/entitlement_key_session.h

@@ -21,7 +21,7 @@ class EntitlementKeySession : public ContentKeySession {
                         metrics::CryptoMetrics* metrics);
   ~EntitlementKeySession() override {}
 
-  KeySessionType Type() { return kEntitlement; }
+  KeySessionType Type() override { return kEntitlement; }
 
   // Load Keys for ContentKeySession
   OEMCryptoResult LoadKeys(const std::string& message,