ci: reduce nightly version update from semiweekly to weekly

apoelstra · apoelstra · commit b5433ca19296 · 2025-08-22T18:51:14.000Z
Turns out it's hard with GA to do things every other week (or every four weeks).
But it's easy to at least stop doing it twice every week!
diff --git a/.github/workflows/cron-weekly-update-nightly.yml b/.github/workflows/cron-weekly-update-nightly.yml
@@ -1,7 +1,7 @@
 name: Update Nightly rustc
 on:
   schedule:
-    - cron: "5 0 * * 1,4" # runs every Monday and Thursday at 00:05 UTC
+    - cron: "5 0 * * 1" # runs every Monday at 00:05 UTC
   workflow_dispatch: # allows manual triggering
 jobs:
   format:
