Bug 1492671 - Disable screenshot capturing for triggering network requests in payments mochitests r=MattN

Differential Revision: https://phabricator.services.mozilla.com/D8877

--HG--
extra : moz-landing-system : lando

browser/components/payments/test/browser/browser.ini

@@ -1,6 +1,7 @@
 [DEFAULT]
 head = head.js
 prefs =
+  browser.pagethumbnails.capturing_disabled=true
   dom.payments.request.enabled=true
 skip-if = !e10s # Bug 1365964 - Payment Request isn't implemented for non-e10s
 support-files =