upgrade Alabaster theme to 0.7.16 release

[github-actions[bot]]

The backport to branch-8-0 failed:

The process '/usr/bin/git' failed with exit code 1

stderr

``` error: could not apply 3251a9fd... upgrade Alabaster theme hint: After resolving the conflicts, mark them with hint: "git add/rm ", then run hint: "git cherry-pick --continue". hint: You can instead skip this commit with "git cherry-pick --skip". hint: To abort and get back to the state before "git cherry-pick", hint: run "git cherry-pick --abort". ```

stdout

``` Auto-merging requirements.txt CONFLICT (content): Merge conflict in requirements.txt ```

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-branch-8-0 branch-8-0
# Navigate to the new working tree
cd .worktrees/backport-branch-8-0
# Create a new branch
git switch --create backport-868-to-branch-8-0
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick 3251a9fd7597b8516d6a22acdbe40c468e87e53f,d00e9f87cc1088d249f419def449d2a9438c428e
# Push it to GitHub
git push --set-upstream origin backport-868-to-branch-8-0
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-branch-8-0

Then, create a pull request where the base branch is branch-8-0 and the compare/head branch is backport-868-to-branch-8-0.