Revert "Revert matrix changes"

This reverts commit 1b00075.

Author: wtgodbe

.azure/pipelines/helix-matrix.yml

@@ -1,6 +1,13 @@
 # We only want to run full helix matrix on main
-pr: none
 trigger: none
+pr:
+  branches:
+    include:
+    - main
+  paths:
+    include:
+    - src/Servers/IIS/**/*
+    - src/Servers/HttpSys/**/*
 schedules:
 # Cron timezone is UTC.
 - cron: "0 */12 * * *"