fix(browser): dispose tester iframe on done (#5595)

Author: hi-ogawa

Diff for: packages/browser/src/client/main.ts

@@ -69,6 +69,10 @@ client.ws.addEventListener('open', async () => {
         const filenames = e.data.filenames
         filenames.forEach(filename => runningFiles.delete(filename))
 
+        const iframeId = filenames.length > 1 ? ID_ALL : filenames[0]
+        iframes.get(iframeId)?.remove()
+        iframes.delete(iframeId)
+
         if (!runningFiles.size)
           await done()
         break