misc: update readthedocs config (libuv#4009)

vtjnash · web-flow · commit 4e766761d007 · 2023-05-20T09:36:23.000-04:00
Now required: https://docs.readthedocs.io/en/stable/config-file/v2.html#build-os
diff --git a/.readthedocs.yaml b/.readthedocs.yaml
@@ -6,6 +6,7 @@ sphinx:
   fail_on_warning: false
 
 build:
+  os: "ubuntu-22.04"
   tools:
     python: "3.9"
 
