Run screenshot tests daily, instead of on each commit (#10426)

* Stop running Percy on develop builds

Instead, we will run it daily. This will reduce the number of Percy
tests we run each month.

* Run screenshot tests daily

* Prettier for percy_daily.yml

* Maybe something like this

.github/workflows/element-web.yaml

@@ -3,6 +3,8 @@
 # as an artifact and run integration tests.
 name: Element Web - Build
 on:
+    schedule:
+        - cron: "17 4 * * *" # every day at 04:17 UTC
     pull_request: {}
     push:
         branches: [develop, master]