[doc] set default python env to 3.10

we stop supporting building with python 3.9 now

Signed-off-by: Lonnie Liu <lonnie@anyscale.com>

Author: aslonnie

doc/source/ray-contribute/development.rst

@@ -40,7 +40,7 @@ Create a virtual environment to prevent version conflicts and to develop with an
 
         .. code-block:: shell
 
-            conda create -c conda-forge python=3.9 -n myenv
+            conda create -c conda-forge python=3.10 -n myenv
 
 
         Activate your virtual environment to tell the shell/terminal to use this particular Python:

doc/source/ray-observability/ray-distributed-debugger.rst

@@ -30,7 +30,7 @@ Create a new virtual environment and install dependencies.
 .. testcode::
     :skipif: True
 
-    conda create -n myenv python=3.9
+    conda create -n myenv python=3.10
     conda activate myenv
     pip install "ray[default]" debugpy
 

doc/source/ray-overview/installation.rst

@@ -273,7 +273,7 @@ Ray can also be installed as a conda package on Linux and Windows.
 .. code-block:: bash
 
   # also works with mamba
-  conda create -c conda-forge python=3.9 -n ray
+  conda create -c conda-forge python=3.10 -n ray
   conda activate ray
 
   # Install Ray with support for the dashboard + cluster launcher