📝🔧 Upgrade the RTD configuration

The new config schema is stricter and the old one will stop working
soon.

.readthedocs.yml

@@ -1,10 +1,19 @@
-version: 2
+---
 
-formats: all
+version: 2
 
 build:
-  image: latest
+  os: ubuntu-22.04
+  tools:
+    python: 3.7
+
 python:
-  version: 3.7
   install:
   - requirements: requirements/doc.txt
+
+sphinx:
+  builder: dirhtml
+  configuration: docs/conf.py
+  fail_on_warning: true
+
+...