renovate: move scheduled updates to Sunday

https://docs.renovatebot.com/configuration-options/#schedule

Schedule: "on Monday" pretty much means "submit PRs all throughout
Monday". That means if we merge Renovate PRs on Monday morning, we will
still get more throughout the day.

Instead, send the scheduled PRs on Sunday so that they're ready for
merging on Monday.

Note: currently, only GH actions and appstudio-utils updates are on a
schedule. Others are unscheduled.

Signed-off-by: Adam Cmiel <[email protected]>

renovate.json

@@ -23,7 +23,7 @@
         "quay.io/konflux-ci/appstudio-utils"
       ],
       "schedule": [
-        "on monday"
+        "on sunday"
       ]
     },
     {
@@ -139,7 +139,7 @@
         ".github/workflows/**"
       ],
       "schedule": [
-        "on monday"
+        "on sunday"
       ]
     },
     {