Update README.md

The explanation already says that you cannot use PactVerificationSpringProvider without @WebMvcTest annotation. Therefore it falls into PactVerificationInvocationContextProvider extension.

provider/junit5spring/README.md

@@ -83,7 +83,7 @@ For example:
 class MockMvcTestTargetStandaloneMockMvcTestJava {
 
     @TestTemplate
-    @ExtendWith(PactVerificationSpringProvider.class)
+    @ExtendWith(PactVerificationInvocationContextProvider.class)
     void pactVerificationTestTemplate(PactVerificationContext context) {
         context.verifyInteraction();
     }