Dynamically enable Style/SingleLineDoEndBlock

This enables `Style/SingleLineDoEndBlock` for consumers on a new enough
version of RuboCop. This allows us to enable the cop without dropping
support for old RuboCop versions.

rubocop.yml

@@ -1,3 +1,5 @@
+<% rubocop_version = Gem.loaded_specs.fetch("rubocop").version %>
+
 inherit_mode:
   merge:
   - Exclude
@@ -794,6 +796,11 @@ Style/SelectByRegexp:
 Style/SingleArgumentDig:
   Enabled: false
 
+<% if rubocop_version >= Gem::Version.new('1.57') %>
+Style/SingleLineDoEndBlock:
+  Enabled: true
+<% end %>
+
 Style/SlicingWithRange:
   Enabled: false
 

test/fixtures/full_config.yml

@@ -3943,7 +3943,7 @@ Style/SingleLineBlockParams:
     - elem
 Style/SingleLineDoEndBlock:
   Description: Checks for single-line `do`...`end` blocks.
-  Enabled: pending
+  Enabled: true
   VersionAdded: '1.57'
 Style/SingleLineMethods:
   Description: Avoid single-line methods.