ci: Disable docs-only build for missing azure devops feature

https://developercommunity.visualstudio.com/content/idea/1156360/report-status-to-github-for-pipelines-that-do-not.html

.vsts-ci.yml

@@ -17,7 +17,6 @@ pr:
     include:
     - '/'
     exclude:
-    - 'doc/'
     - .dependabot/
     - .github/
     - .editorconfig