Don't run global docs build on schedule

Author: ChrisRackauckas

.buildkite/documentation.yml

@@ -28,7 +28,7 @@ steps:
     env:
       DATADEPS_ALWAYS_ACCEPT: true
       JULIA_DEBUG: "Documenter"
-    if: build.message !~ /\[skip docs\]/ && !build.pull_request.draft
+    if: build.message !~ /\[skip docs\]/ && !build.pull_request.draft && build.source != "schedule"
     timeout_in_minutes: 2000
 
 env: