Upgraded to Python 3.12, Ubuntu 24.04, and enabled fail_on_warning for docs builds.

.github/workflows/docs.yml

@@ -21,8 +21,7 @@ permissions:
 
 jobs:
   docs:
-    # OS must be the same as on djangoproject.com.
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-24.04
     name: docs
     steps:
       - name: Checkout

.readthedocs.yml

@@ -4,12 +4,13 @@
 version: 2
 
 build:
-  os: ubuntu-20.04
+  os: ubuntu-24.04
   tools:
-    python: "3.8"
+    python: "3.12"
 
 sphinx:
   configuration: docs/conf.py
+  fail_on_warning: true
 
 python:
   install: