Auto-redirect to latest docs version doesn't work for some legacy branch tutorials which were renamed or removed

**Your Godot version:**
3.4

**Issue description:**
When accessing links via google, the page is often outdated, giving a link to the newer version. This is OK but then when clicking the link the browser is not redirected to the correct page:

**URL to the documentation page:**
https://docs.godotengine.org/en/2.1/learning/features/lighting/shadow_mapping.html

Should lead to

https://docs.godotengine.org/en/3.4/tutorials/3d/lights_and_shadows.html#shadow-mapping