ci: doc-build: use customer runner

Apparently the PDF build needs more resources, otherwise we end up
aborting the build too early.

Signed-off-by: Anas Nashif <[email protected]>

Author: nashif

.github/workflows/doc-build.yml

@@ -117,7 +117,7 @@ jobs:
   doc-build-pdf:
     name: "Documentation Build (PDF)"
     if: github.event_name != 'pull_request'
-    runs-on: ubuntu-22.04
+    runs-on: zephyr-runner-linux-x64-4xlarge
     container: texlive/texlive:latest
     timeout-minutes: 60
     concurrency: