Limit the Renovate schedule to the early hours of the scheduled Wednesday

The "every 2 weeks on wednesday" schedule opened a window for the whole day,
so after the group PR was merged Renovate kept running and raised new PRs on
the same branch for versions that passed minimumReleaseAge later that day
(e.g. #6282 followed by #6286 and #6293).

Restrict every schedule to before 4:00 am UTC so each group produces a single
PR per cycle. The "4:00 am" form is required, later.js silently drops the time
constraint for "4am" in this position.

renovate.json

@@ -17,14 +17,14 @@
       "matchManagers": ["xcodegen"],
       "groupName": "Project Dependencies",
       "schedule": [
-          "every 2 weeks on wednesday",
+          "every 2 weeks on wednesday before 4:00 am",
       ]
     },
     {
       "matchManagers": ["swift"],
       "groupName" : "Tool Dependencies",
       "schedule": [
-          "every 2 weeks on wednesday",
+          "every 2 weeks on wednesday before 4:00 am",
       ]
     },
     {
@@ -32,7 +32,7 @@
       "matchFileNames": ["compound-ios/Package.swift"],
       "groupName": "Compound Dependencies",
       "schedule": [
-          "every 2 weeks on wednesday",
+          "every 2 weeks on wednesday before 4:00 am",
       ]
     },
     {
@@ -40,7 +40,7 @@
       "matchPackageNames": ["pointfreeco/swift-snapshot-testing", "https://github.com/pointfreeco/swift-snapshot-testing"],
       "groupName": "Shared Dependencies",
       "schedule": [
-          "every 2 weeks on wednesday",
+          "every 2 weeks on wednesday before 4:00 am",
       ]
     },
   ]