Update release branch CI to trigger manually (#10445)

Updates a condition from #10438 to trigger historical release CI on
manual trigger, not just the schedule.

Author: alexcrichton

.github/workflows/ci-cron-trigger.yml

@@ -50,4 +50,4 @@ jobs:
         name: Trigger release branch CI weekly
         env:
           GH_TOKEN: ${{ github.token }}
-        if: github.event.schedule == '34 2 * * 1'
+        if: "github.event.schedule == '34 2 * * 1' || !github.event.schedule"