External CI: Add triggers for mainline branch (#388)

.azuredevops/rocm-ci.yml

@@ -14,6 +14,7 @@ trigger:
   branches:
     include:
     - develop
+    - mainline
   paths:
     exclude:
     - .github
@@ -28,6 +29,7 @@ pr:
   branches:
     include:
     - develop
+    - mainline
   paths:
     exclude:
     - .github