github: limit doc deploy to just pkgcore/pkgcore repository

For a proper fork/PR it's best to show things building properly,
and a deploy will never succeed.  Confirm docs build and skip
the deploy for folks who've got forks.

Signed-off-by: Brian Harring <ferringb@gmail.com>

Author: ferringb

.github/workflows/doc.yml

@@ -44,6 +44,7 @@ jobs:
         path: build/sphinx/html
 
   deploy:
+    if: github.repository == 'pkgcore/pkgcore'
     environment:
       name: github-pages
       url: ${{ steps.deployment.outputs.page_url }}