ci: Fix sveltekit flakes (#12327)

Observed a flake here:
https://github.com/getsentry/sentry-javascript/actions/runs/9348183996/job/25727088799?pr=12267#step:12:92

Author: Luca Forstner

dev-packages/e2e-tests/test-applications/sveltekit-2-svelte-5/tests/performance.test.ts

@@ -193,7 +193,7 @@ test.describe('performance events', () => {
       return txnEvent?.contexts?.trace?.op === 'navigation' && txnEvent?.tags?.runtime === 'browser';
     });
 
-    await page.goto('/');
+    await waitForInitialPageload(page, { route: '/' });
 
     const navigationClickPromise = page.locator('#routeWithParamsLink').click();
 
@@ -252,8 +252,6 @@ test.describe('performance events', () => {
   });
 
   test('captures one navigation transaction per redirect', async ({ page }) => {
-    await page.goto('/');
-
     const clientNavigationRedirect1TxnPromise = waitForTransaction('sveltekit-2-svelte-5', txnEvent => {
       return (
         txnEvent?.contexts?.trace?.op === 'navigation' &&
@@ -278,6 +276,8 @@ test.describe('performance events', () => {
       );
     });
 
+    await waitForInitialPageload(page, { route: '/' });
+
     const navigationClickPromise = page.locator('#redirectLink').click();
 
     const [redirect1TxnEvent, redirect2TxnEvent, redirect3TxnEvent, _] = await Promise.all([

dev-packages/e2e-tests/test-applications/sveltekit-2/tests/performance.test.ts

@@ -193,7 +193,7 @@ test.describe('performance events', () => {
       return txnEvent?.contexts?.trace?.op === 'navigation' && txnEvent?.tags?.runtime === 'browser';
     });
 
-    await page.goto('/');
+    await waitForInitialPageload(page, { route: '/' });
 
     const navigationClickPromise = page.locator('#routeWithParamsLink').click();
 
@@ -252,8 +252,6 @@ test.describe('performance events', () => {
   });
 
   test('captures one navigation transaction per redirect', async ({ page }) => {
-    await page.goto('/');
-
     const clientNavigationRedirect1TxnPromise = waitForTransaction('sveltekit-2', txnEvent => {
       return (
         txnEvent?.contexts?.trace?.op === 'navigation' &&
@@ -278,6 +276,8 @@ test.describe('performance events', () => {
       );
     });
 
+    await waitForInitialPageload(page, { route: '/' });
+
     const navigationClickPromise = page.locator('#redirectLink').click();
 
     const [redirect1TxnEvent, redirect2TxnEvent, redirect3TxnEvent, _] = await Promise.all([