CI: no need for extra requirement file for RTD, and bump python version

Author: bsipocz

.readthedocs.yml

@@ -13,7 +13,7 @@ sphinx:
 build:
   os: ubuntu-22.04
   tools:
-    python: "3.10"
+    python: "3.12"
   apt_packages:
     - graphviz
   jobs:
@@ -22,7 +22,6 @@ build:
 
 python:
   install:
-    - requirements: docs/requirements.txt
     - method: pip
       path: .
       extra_requirements: