More fixes for system root certs.

Author: kannanjgithub

xds/src/test/java/io/grpc/xds/internal/security/certprovider/CertProviderClientSslContextProviderTest.java

@@ -206,7 +206,7 @@ public void testProviderForClient_systemRootCerts_regularTls() {
 
     assertThat(provider.savedKey).isNull();
     assertThat(provider.savedCertChain).isNull();
-    assertThat(provider.savedTrustedRoots).isNull();
+    assertThat(provider.savedTrustedRoots).isNotNull();
     assertThat(provider.getSslContext()).isNotNull();
     TestCallback testCallback =
         CommonTlsContextTestsUtil.getValueThruCallback(provider);