chore(deps): update dependency ruby-version to v4

Author: renovate[bot]

.readthedocs.yaml

@@ -7,7 +7,7 @@ version: 2
 build:
   os: ubuntu-26.04
   tools:
-    ruby: "3.3"
+    ruby: "4.0"
   jobs:
     install:
       - chmod +x "./scripts/readthedocs_build.sh"