Bug 1707823 - [devtools] Make navigateTo more secure. r=ochameau.

In the `BrowserTestUtils.browserLoaded` call we use in `navigateTo`, we weren't
checking for a specific uri to be loaded, which means the Promise could resolve
on *any* page being loaded.
This patch makes it more secure by waiting the load event for the uri we navigated to.

Differential Revision: https://phabricator.services.mozilla.com/D113479

devtools/client/shared/test/shared-head.js

@@ -491,8 +491,10 @@ async function navigateTo(uri, { isErrorPage = false } = {}) {
   const currentBrowsingContextID = browser.browsingContext.id;
   const onBrowserLoaded = BrowserTestUtils.browserLoaded(
     browser,
+    // includeSubFrames
     false,
-    null,
+    // resolve on this specific page to load (if null, it would be any page load)
+    uri,
     isErrorPage
   );
   BrowserTestUtils.loadURI(browser, uri);