Merge branch 'book-v1-redirects' into gh-pages

Let's integrate this into my fork so that it is deployed to
https://dscho.github.io/git-scm.com (to be able to play around with it).

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

Diff for: .github/workflows/update-book.yml

@@ -52,9 +52,12 @@ jobs:
         with:
           sparse-checkout: |
             script
+            data/
             external/book/sync
             external/book/data
             external/book/content/book/${{ matrix.language.lang }}
+            external/book/content/book${{ matrix.language.lang != 'en' && '/en' || '' }}
+            external/book/content/book${{ matrix.language.lang != 'en' && '/en' || 'v1' }}
             external/book/static/book/${{ matrix.language.lang }}
       - name: clone ${{ matrix.language.repository }}
         run: |