Update TMCH root certificate (#1918)

See b/260945047.

Also refactored the corresponding tests, which should future updates easier.

This change should be deployed at or around 2023-02-15T16:00:00Z.

util/src/main/java/google/registry/util/ResourceUtils.java

@@ -26,6 +26,8 @@ import java.net.URL;
 /** Utility methods related to reading java resources. */
 public final class ResourceUtils {
 
+  private ResourceUtils() {}
+
   /** Loads a resource from a file as a string, assuming UTF-8 encoding. */
   public static String readResourceUtf8(String filename) {
     return readResourceUtf8(getResource(filename));