D2: give the memory-leak reproducer's fake request isNavigationRequest()

wirePageEvents now runs the navigation guard on every request event; the
fake request adapter supplies the method real Playwright requests have.

browse/test/memory-leak-reproducer.test.ts

@@ -97,6 +97,7 @@ describe('memory-leak reproducer: requestfinished does not materialize bodies',
       page.emit('request', {
         url: () => `https://example.invalid/asset/${i}`,
         method: () => 'GET',
+        isNavigationRequest: () => false,
       });
     }