Bump to ubuntu-24.04 and mambaforge-23.11 in ReadTheDocs (#51)

Xref https://docs.readthedocs.io/en/stable/config-file/v2.html#build-os and https://docs.readthedocs.io/en/stable/config-file/v2.html#build-tools-python

Author: weiji14

.readthedocs.yml

@@ -2,9 +2,9 @@
 version: 2
 
 build:
-  os: "ubuntu-20.04"
+  os: "ubuntu-24.04"
   tools:
-    python: "mambaforge-4.10"
+    python: "mambaforge-23.11"
 
 # Optionally set the version of Python and requirements required to build your docs
 conda: