Skip some cast tests if not supported

Merged from https://widevine-internal-review.googlesource.com/190072

Change-Id: I4134b3f090e3f47c80601ae30262d0587808e88a

libwvdrmengine/oemcrypto/test/oemcrypto_cast_test.h

@@ -73,6 +73,9 @@ class OEMCryptoLoadsCertificateAlternates : public OEMCryptoLoadsCertificate {
 
   // If force is true, we assert that the key loads successfully.
   void LoadCastCertificateKey(bool force) {
+    if (!wvoec::global_features.cast_receiver) {
+      GTEST_SKIP() << "Cast not supported";
+    }
     // Padding scheme used to sign cast data.
     constexpr uint32_t schemes = kSign_PKCS1_Block1;
     // prov 2 or prov 3