[FIX] contributing: dead idiomatic python link

The link replaced is dead and doesn't lead to anything anymore. The new link is
the exact same page but hosted on another website.

closes #12541

Signed-off-by: Antoine Vandevenne (anv) <[email protected]>

Author: Megaaaaaa

content/contributing/development/coding_guidelines.rst

@@ -575,7 +575,7 @@ So, you can write ``if some_collection:`` instead of ``if len(some_collection):`
 - As a good developer, document your code (docstring on methods, simple
   comments for tricky part of code)
 - In additions to these guidelines, you may also find the following link
-  interesting: http://python.net/~goodger/projects/pycon/2007/idiomatic/handout.html
+  interesting: https://david.goodger.org/projects/pycon/2007/idiomatic/handout.html
   (a little bit outdated, but quite relevant)
 
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