[ci][docs] Add a pull request trigger for the doxygen CI job.

This job triggers if root-docs-ci.yml or the doxygen folder are touched.

Author: hageboeck

.github/workflows/root-docs-ci.yml

@@ -1,9 +1,13 @@
 name: 'ROOT Docs CI'
 
 on:
+  pull_request:
+    paths:
+      - '.github/workflows/root-docs-ci.yml'
+      - 'documentation/doxygen/**'
+    branches:
+      - 'master'
 
-  # Allows nightly builds to trigger one run for each branch easily, by
-  # providing the relevant branch as "default" value here:
   workflow_call:
     inputs:
       incremental:
@@ -84,12 +88,13 @@ jobs:
       run: ".github/workflows/root-ci-config/build_root.py
                   --buildtype      Release
                   --platform       ${{ env.PLATFORM }}
-                  --incremental    ${{ inputs.incremental }}
+                  --incremental    ${{ inputs.incremental == null && 'false' || inputs.incremental }}
                   --base_ref       ${BASE_REF}
                   --head_ref       ${BASE_REF}
-                  --binaries       false
                   --repository     ${{ github.server_url }}/${{ github.repository }}
-                  --overrides      ${OVERRIDES}"
+                  --overrides      ${OVERRIDES}
+                  --upload-artifacts false
+                  --binaries         false"
 
     - name: Run Doxygen
       working-directory: ${{ env.DOC_LOCATION }}