[ci] Add trigger for the 6.38 doc

Author: dpiparo

.github/workflows/root-docs-638.yml

@@ -0,0 +1,23 @@
+name: 'ROOT Docs 6.38'
+
+on:
+  schedule:
+    - cron: '0 1 * * *'
+
+  workflow_dispatch:
+    inputs:
+      incremental:
+        description: 'Do incremental build'
+        type: boolean
+        required: true
+        default: true
+      # docu_input: # opportunity: overwrite makeinput.sh with these args
+      #   description: Folders to build documentation for. All folders are built if empty.
+      #   type: string
+      #   default: ""
+      #   required: false
+
+jobs:
+  run_nightlies:
+    uses: root-project/root/.github/workflows/root-docs-ci.yml@v6-38-00-patches
+    secrets: inherit