Update rtd build env to 3.11 [skip ci]

Author: aphearin

.readthedocs.yaml

@@ -5,7 +5,7 @@ build:
   apt_packages:
     - graphviz
   tools:
-    python: "3.10"
+    python: "3.11"
 
 sphinx:
   configuration: docs/conf.py

docs/installing_halotools_with_virtualenv.rst

@@ -12,7 +12,7 @@ create a virtual environment that will automatically have compatible versions of
 By installing into a virtual environment, you will not change any of the
 packages that are already installed system-wide on your machine. In the example below, we will use conda to create a virtual environment with all the dependencies handled automatically::
 
-    conda create -n htenv python=3.9 halotools=0.8 h5py ipython jupyter matplotlib
+    conda create -n htenv python=3.11 halotools=0.9 h5py ipython jupyter matplotlib
 
 In order to activate this environment::