Update SimPEG version to 0.23

Update `environment.yml` and the admonition in the landing page.

Author: santisoler

environment.yml

@@ -9,6 +9,6 @@ dependencies:
   # Notebook requirements
   - jupyter
   - nbconvert
-  - simpeg==0.22.*
+  - simpeg==0.23.*
   - discretize==0.10.*
   - pymatsolver

index.md

@@ -10,7 +10,7 @@ SimPEG user tutorials is the place for those who have [installed SimPEG](https:/
 
 
 :::{caution} Caution
-These user tutorials are meant to be run with SimPEG v0.22. Please, make sure
+These user tutorials are meant to be run with SimPEG v0.23. Please, make sure
 you have this version installed.
 :::