[CI] Run nigthly at 4am, to avoid conflicts with UR's perf job

Author: lukaszstolarczuk

.github/workflows/nightly.yml

@@ -1,11 +1,11 @@
 # Various non-standard tests, requiring e.g. longer run
 name: Nightly
 
-# This job is run at 00:00 UTC every day or on demand.
+# This job is run at 04:00 UTC every day or on demand.
 on:
   workflow_dispatch:
   schedule:
-    - cron:  '0 0 * * *'
+    - cron: '0 4 * * *'
 
 permissions:
   contents: read