Updating unit test for error code common PR (#2147)

### Summary
See
AzureAD/microsoft-authentication-library-common-for-android#2460.
With the null_pointer_error code, this unit test needs to be updated to
compare with the null_pointer_error code vs the unknown_error code.

Author: melissaahn

common

@@ -200,7 +200,7 @@ public void testAcquireTokenFailureUnsuccessfulTokenResult() {
                 .withLoginHint(username)
                 .withScopes(Arrays.asList(mScopes))
                 .fromAuthority(getAuthority())
-                .withCallback(AcquireTokenTestHelper.failureInteractiveCallback(ErrorCodes.UNKNOWN_ERROR_CODE))
+                .withCallback(AcquireTokenTestHelper.failureInteractiveCallback(ErrorCodes.NULL_POINTER_ERROR_CDOE))
                 .build();
 
         mApplication.acquireToken(parameters);

msal/src/test/java/com/microsoft/identity/client/e2e/tests/mocked/AcquireTokenMockTest.java

@@ -29,4 +29,5 @@ public class ErrorCodes {
     public static final String NO_ACCOUNT_FOUND_ERROR_CODE = "no_account_found";
     public static final String NO_CURRENT_ACCOUNT_ERROR_CODE = "no_current_account";
     public static final String INTERNAL_SERVER_ERROR_CODE = "internal_server_error";
+    public static final String NULL_POINTER_ERROR_CDOE = "null_pointer_error";
 }