update rtd.yml file

Signed-off-by: foamyguy <foamyguy@gmail.com>

Author: FoamyGuy

.readthedocs.yaml

@@ -12,7 +12,7 @@ sphinx:
  configuration: docs/conf.py
 
 build:
- os: ubuntu-20.04
+ os: ubuntu-lts-latest
  tools:
  python: "3"