fix: use jupiter assertion

Author: diegomarquezp

sdk-platform-java/gapic-generator-java/src/test/java/com/google/api/generator/gapic/protoparser/HttpRuleParserTest.java

@@ -16,6 +16,7 @@
 
 import static com.google.common.truth.Truth.assertThat;
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertThrows;
 import static org.junit.Assert.assertTrue;
 
 import com.google.api.generator.gapic.model.HttpBindings;