Add docfx verification to build

Author: AArnott

.github/workflows/build.yml

@@ -3,8 +3,8 @@ name: CI
 on:
   push:
     branches:
-      - main
-      - validate/*
+    - main
+    - validate/*
   pull_request:
 
 env:
@@ -51,6 +51,9 @@ jobs:
       run: dotnet format --verify-no-changes --no-restore
       shell: pwsh
       if: runner.os == 'Linux'
+    - name: 📚 Verify docfx build
+      run: dotnet docfx docfx/docfx.json --warningsAsErrors --disableGitFeatures
+      if: runner.os == 'Linux'
     - name: ⚙ Update pipeline variables based on build outputs
       run: azure-pipelines/variables/_pipelines.ps1
       shell: pwsh