RTD: Change OS image to Ubuntu 22.04

mhilbrunner · web-flow · commit 1564341fcabe · 2023-05-05T15:21:10.000+02:00
This should hopefully fix build errors due to a recent OpenSSL change in urllib3
diff --git a/.readthedocs.yml b/.readthedocs.yml
@@ -5,7 +5,7 @@
 version: 2
 
 build:
-  image: latest
+  os: ubuntu-22.04
 
 sphinx:
   configuration: conf.py
