update django docs links from 5.0 to 5.1

Author: Xronophobe

chapter_19_spiking_custom_auth.asciidoc

@@ -203,7 +203,7 @@ The login in theory will be something like this:
 // "...and if so, we authorize/approve the request to authenticate/log in as the
 // associated user"
 
-// https://docs.djangoproject.com/en/5.0/topics/auth/customizing/
+// https://docs.djangoproject.com/en/5.1/topics/auth/customizing/
 
 
 First let's prep an app for our accounts stuff:
@@ -487,7 +487,7 @@ we need to sort out user authentication in Django.
 // reason behind it.
 The first thing we'll need is a user model.
 I took a dive into the
-https://docs.djangoproject.com/en/5.0/topics/auth/customizing[Django
+https://docs.djangoproject.com/en/5.1/topics/auth/customizing[Django
 auth documentation] and tried to hack in the simplest possible one:
 
 [role="sourcecode"]