fix: snap flakiness on installSnapSimpleKeyring function (#26039)

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## **Description**

There is a race condition where we click `Create Account` on the snap
dapp, before the popup for Connecting hasn't been closed (see video
below). This causes that the click for Create Account has no effect and
the dialog never opens, with the error:
`Error: No window with title: MetaMask Dialog` - example of failure
[here](https://app.circleci.com/pipelines/github/MetaMask/metamask-extension/92347/workflows/a12a664d-4eb8-4c49-a57c-1e58cb49361f/jobs/3437511/tests)
in the Remove Account Snap

The fix is to wait until the popup is closed before continue.
This source of flakiness can affect several snap tests (all the tests
that use the `installSnapSimpleKeyring` function).

Note: this does not mitigate the current Snap Account issues that we see
on ci, but does fix a source of flakiness introduced in this function
(I've been able to reproduce the flakiness locally and saw mitigated
after the fix, for the Remove Account test).

[![Open in GitHub
Codespaces](https://github.com/codespaces/badge.svg)](https://codespaces.new/MetaMask/metamask-extension/pull/26039?quickstart=1)

## **Related issues**

Fixes:

## **Manual testing steps**

1. Check ci

## **Screenshots/Recordings**
Notice how, we start interacting with the dapp again, but the popup
hasn't been closed yet (second ~22)


https://github.com/user-attachments/assets/fbfe4281-9b1a-4311-bca3-6e746e965109




<!-- [screenshots/recordings] -->

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## **Pre-merge reviewer checklist**

- [ ] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
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test/e2e/accounts/common.ts

@@ -85,6 +85,9 @@ export async function installSnapSimpleKeyring(
     tag: 'button',
   });
 
+  // Wait until popup is closed before proceeding
+  await driver.waitUntilXWindowHandles(2);
+
   await driver.switchToWindowWithTitle(WINDOW_TITLES.SnapSimpleKeyringDapp);
 
   await driver.waitForSelector({

test/e2e/accounts/create-snap-account.spec.ts

@@ -49,6 +49,9 @@ describe('Create Snap Account', function (this: Suite) {
           tag: 'button',
         });
 
+        // Wait until popup is closed before proceeding
+        await driver.waitUntilXWindowHandles(2);
+
         // move back to the Snap window to test the create account flow
         await driver.switchToWindowWithTitle(
           WINDOW_TITLES.SnapSimpleKeyringDapp,
@@ -128,6 +131,9 @@ describe('Create Snap Account', function (this: Suite) {
           tag: 'button',
         });
 
+        // Wait until popup is closed before proceeding
+        await driver.waitUntilXWindowHandles(2);
+
         // move back to the Snap window to test the create account flow
         await driver.switchToWindowWithTitle(
           WINDOW_TITLES.SnapSimpleKeyringDapp,
@@ -220,6 +226,9 @@ describe('Create Snap Account', function (this: Suite) {
           tag: 'button',
         });
 
+        // Wait until popup is closed before proceeding
+        await driver.waitUntilXWindowHandles(2);
+
         // move back to the Snap window to test the create account flow
         await driver.switchToWindowWithTitle(
           WINDOW_TITLES.SnapSimpleKeyringDapp,