Rebrand advanced pipeline into nightly pipeline, running only master on schedule. Move release branch tests to advanced-test pipeline.

.azure-pipelines/advanced-test.yml

@@ -1,5 +1,6 @@
-# Advanced pipeline for running our full test suite on demand.
+# Advanced pipeline for running our full test suite on demand and for release branches.
 trigger:
+  - '*.x'
   # When changing these triggers, please ensure the documentation under
   # "Running tests in CI" is still correct.
   - azure-test-*
@@ -8,3 +9,6 @@ pr: none
 
 stages:
   - template: templates/stages/test-and-package-stage.yml
+  # Notify failures only for release branches.
+  - template: templates/stages/notify-failure-stage.yml
+    condition: and(failed(), endsWith(variables['Build.SourceBranchName', '.x'])

.azure-pipelines/nightly.yml

@@ -1,8 +1,6 @@
-# Advanced pipeline for running our full test suite on protected branches.
-trigger:
-  - '*.x'
+# Nightly pipeline running each day for master.
+trigger: none
 pr: none
-# This pipeline is also nightly run on master
 schedules:
   - cron: "0 4 * * *"
     displayName: Nightly build