Change an ASSERT to an EXPECT

Merge from widevine repo of http://go/wvgerrit/17202

This allows more checks in the test to run.  Returning the correct
error code is less important than the next check, which verifies the
signature was not computed.

This helps diagnose b/21708882, but does not fix it.

b/27787064

Change-Id: I65306c54b77370951bc54e8ef9f6140f58bea32c

libwvdrmengine/oemcrypto/test/oemcrypto_test.cpp

@@ -3389,7 +3389,7 @@ class OEMCryptoLoadsCertificateAlternates : public OEMCryptoLoadsCertificate {
                                            &signature_length, scheme);
     }
 
-    ASSERT_NE(OEMCrypto_SUCCESS, sts)
+    EXPECT_NE(OEMCrypto_SUCCESS, sts)
         << "Signed with forbidden padding scheme=" << (int)scheme
         << ", size=" << (int)size;
     vector<uint8_t> zero(signature_length, 0);