[ci] Build doc for 6.38

Simiar to commit 432c8f5 for 6.36.

Author: hahnjo

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

@@ -34,11 +34,11 @@ jobs:
 
     env:
       PLATFORM: alma9
-      DOC_DIR: master
+      DOC_DIR: v6-38-00-patches
       DOC_LOCATION: /github/home
-      BASE_REF: master
-      WEB_DIR_NAME: master
-      TAR_NAME: htmlmaster.tar
+      BASE_REF: v6-38-00-patches
+      WEB_DIR_NAME: v638
+      TAR_NAME: html638.tar
 
     permissions:
       contents: read