Update Code Climate Rubocop version

Code Climate was failing to analyze our repo because their rubocop 1.31
doesn't support rubocop-capybara.

Since we're using rubocop 1.56.4 in our code, we're going to use
version 1.56.3 for Code Climate which, at the time of writing, is the
latest available version in Code Climate.

.codeclimate.yml

@@ -1,7 +1,7 @@
 engines:
   rubocop:
     enabled: true
-    channel: rubocop-1-31-0
+    channel: rubocop-1-56-3
   duplication:
     enabled: true
     config: