Install Evergreen workflow

Co-authored-by: mrjf <180956+mrjf@users.noreply.github.com>

Author: Copilot

.github/workflows/ci.yml

@@ -6,6 +6,7 @@ env:
 on:
   pull_request:
     branches: [ main ]
+  workflow_dispatch:
   # Tier 1 also runs in merge queue context so the same unit + build checks
   # execute against the tentative merge commit that the queue creates. See
   # microsoft/apm#770 for the design.