Rename Python code

The name dark_visitors.py gives the impression that the code is entirely
related to the dark visitors website, whereas the update command relates
to dark visitors and the convert command is unrelated to dark visitors.

.github/workflows/ai_robots_update.yml

@@ -16,7 +16,7 @@ jobs:
           git config --global user.name "dark-visitors"
           git config --global user.email "dark-visitors@users.noreply.github.com"
           echo "Updating robots.json with data from darkvisitor.com ..."
-          python code/dark_visitors.py --update
+          python code/robots.py --update
           echo "... done."
           git --no-pager diff
           git add -A

.github/workflows/main.yml

@@ -25,7 +25,7 @@ jobs:
           git log -1
           git status
           echo "Updating robots.txt and table-of-bot-metrics.md if necessary ..."
-          python code/dark_visitors.py --convert
+          python code/robots.py --convert
           echo "... done."
           git --no-pager diff
           git add -A