Reduce the protocol delay for Chrome in the integration tests

Originally we introduced a small delay for Puppeteer operations in
Chrome to avoid intermittent failures where protocol calls were
happening too quickly in succession. However, since then a number of
improvements were made, both locally and upstream, that reduce the need
for this delay:

- the integration tests have been hardened to remove (potential) sources
  of intermittent failures in many places;
- the browsers and Puppeteer have been updated to improve performance
  and support for testing infrastructure;
- the conversion to WebDriver BiDi has been completed, which replaced
  the Chrome-specific CDP protocol with a formalized protocol that could
  provide more safety guarantees.

This commit therefore reduces the Chrome-specific delay from 5 to 3
milliseconds, which should nowadays be a better value to speed up the
Chrome tests and bring them closer to Firefox in terms of runtime.

test/test.mjs

@@ -992,7 +992,7 @@ async function startBrowser({
     // calls can run before events triggered by the previous protocol calls had
     // a chance to be processed (essentially causing events to get lost). This
     // value gives Chrome a more similar execution speed as Firefox.
-    options.slowMo = 5;
+    options.slowMo = 3;
 
     // avoid crash
     options.args = ["--no-sandbox", "--disable-setuid-sandbox"];