Fix PR build concurrency and stop auto assigning reviewers for draft PRs (#5519)

* build: Remove concurrency

It's called by checks anyway.

* Only assign reviewers for PRs that are ready for reviews

.github/workflows/build.yml

@@ -3,10 +3,6 @@ name: Build job
 on:
   workflow_call:
 
-concurrency:
-  group: pr-builds-${{ github.event.number }}
-  cancel-in-progress: true
-
 env:
   POWERSHELL_TELEMETRY_OPTOUT: 1
   DOTNET_CLI_TELEMETRY_OPTOUT: 1

.github/workflows/pr_triage.yml

@@ -28,6 +28,7 @@ jobs:
           dot: true
 
       - name: Assign reviewers
+        if: ! github.event.pull_request.draft
         run: |
           pip3 install PyGithub
           python3 .github/update_reviewers.py ${{ secrets.GITHUB_TOKEN }} ${{ github.repository }} ${{ github.event.pull_request.number }} .github/reviewers.yml