Bug 1647187 - Update test browser_resources_network_events.js; r=bomsy

Minor test change to keep browser_resources_network_events.js passing with Object.is
comparisons.

Differential Revision: https://phabricator.services.mozilla.com/D85401

devtools/shared/resources/tests/browser_resources_network_events.js

@@ -50,7 +50,7 @@ async function testNetworkEventResourcesWithExistingResources() {
         resourceType: ResourceWatcher.TYPES.NETWORK_EVENT,
         request: {
           url: `${EXAMPLE_DOMAIN}existing_post.html`,
-          method: ["POST"],
+          method: "POST",
         },
         // gets reset based on the type of request
         updates: [],