feat: have Rubocop always enforce shorthand hash syntax (#623)

This was the default since Ruby 3.1 but turns out a year ago [they
changed it to "either"](rubocop/rubocop#13300) -
since we already decided we're in favor of using this syntax when the
rule originally came out, and I don't think there's any value in using
it conditionally, this has Rubocop enforce it again

Author: G-Rath

.rubocop.yml

@@ -190,6 +190,9 @@ Lint/AmbiguousBlockAssociation:
   Exclude:
     - 'spec/**/*'
 
+Style/HashSyntax:
+  EnforcedShorthandSyntax: always
+
 # https://rubocop.readthedocs.io/en/latest/cops_style/
 Style/HashTransformKeys:
   Enabled: false

variants/backend-base/rubocop.yml.tt

@@ -210,6 +210,9 @@ Lint/AmbiguousBlockAssociation:
   Exclude:
     - 'spec/**/*'
 
+Style/HashSyntax:
+  EnforcedShorthandSyntax: always
+
 # https://rubocop.readthedocs.io/en/latest/cops_style/
 Style/HashTransformKeys:
   Enabled: false