readthedocs: Add configuration key build to the readthedocs yaml file.

To fix the error "Config validation error in build.os. Value build not found".

Signed-off-by: Juergen Repp <[email protected]>

.readthedocs.yml

@@ -2,6 +2,10 @@
 # See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
 
 version: 2
+build:
+  os: ubuntu-22.04
+  tools:
+    python: "3"
 sphinx:
   builder: html
   configuration: sphinx/conf.py