run stress tests nightly against staging branches (#113432)

This PR is the first step to address #113372:
- `always: true` should ensure that the nightly run will happen even if there were no recent commits
- The runs should happen against staging branches to make sure changes impact stress runs early

Author: antonfirsov

eng/pipelines/libraries/stress/http.yml

@@ -8,11 +8,11 @@ pr:
 schedules:
 - cron: "0 13 * * *" # 1PM UTC => 5 AM PST
   displayName: HttpStress nightly run
+  always: true
   branches:
     include:
     - main
-    - release/8.0
-    - release/9.0
+    - release/*-staging
 
 variables:
   - template: ../variables.yml

eng/pipelines/libraries/stress/ssl.yml

@@ -8,11 +8,11 @@ pr:
 schedules:
 - cron: "0 13 * * *" # 1PM UTC => 5 AM PST
   displayName: SslStress nightly run
+  always: true
   branches:
     include:
     - main
-    - release/8.0
-    - release/9.0
+    - release/*-staging
 
 variables:
   - template: ../variables.yml