Set low priority for scheduled runs (#70)

Author: castrodd

eng/ci/official-build.yml

@@ -20,7 +20,7 @@ schedules:
 # Build nightly to catch any new CVEs and report SDL often.
 # We are also required to generated CodeQL reports weekly, so this
 # helps us meet that.
-- cron: "0 0 * * *"
+- cron: "0 5 * * *"
   displayName: Nightly Build
   branches:
     include:
@@ -45,6 +45,9 @@ extends:
           name: 1es-pool-azfunc
           image: 1es-ubuntu-22.04
           os: linux
+          ${{ if eq( variables['Build.Reason'], 'Schedule' ) }}:
+            demands:
+            - Priority -equals Low
         sdl:
           sourceAnalysisPool:
             name: 1es-pool-azfunc