Document why surefire config is left untouched with multiple argLine tags

Author: timtebeek

src/main/java/org/openrewrite/java/migrate/AddMockitoJavaAgentToMavenSurefirePlugin.java

@@ -160,6 +160,11 @@ public Xml.Tag visitTag(Xml.Tag tag, ExecutionContext ctx) {
                         return autoFormat(t.withContent(ListUtils.map(pluginContents, c -> c == config ? updatedConfig : c)), ctx);
                     }
                 }
+                // Any remaining case needs no surefire change: either the single argLine already
+                // contains the agent, or there are multiple <argLine> tags. Multiple tags are an
+                // ambiguous configuration, since surefire's argLine is single-valued and only the
+                // first tag is honored; appending another would be silently ignored, so we leave
+                // the configuration untouched rather than guess which argLine to augment.
                 return t;
             }
         });