build: adjust RTD config to explicitly use docs/requirements.txt (#3964)

.readthedocs.yaml

@@ -1,19 +1,15 @@
 version: 2
 
-python:
-  install:
-    - requirements: docs/requirements.txt
-
 build:
   os: ubuntu-24.04
   tools:
-    python: latest
+    python: "3.14"
   jobs:
     # We recommend using a requirements file for reproducible builds.
     # This is just a quick example to get started.
     # https://docs.readthedocs.io/page/guides/reproducible-builds.html
     install:
-      - pip install zensical
+      - pip install -r docs/requirements.txt
     build:
       html:
         - zensical build