Modify email address of commitbot in github actions

.github/workflows/build-docs.yml

@@ -38,7 +38,7 @@ jobs:
  cp generated/* ../docs/
  cd ..
  git config --global user.name 'commitbot'
- git config --global user.email 'commitbot@boost.org'
+ git config --global user.email 'commitbot@example.com'
  git add docs/* || true
  git commit -m "Docs: update from proposal/ md files" || true
  git push