Style/AccessorGrouping: Fix sibling detection for methods with type sigs

- Over in `Homebrew/brew`, trying to enable this cop after
  008506d was released, we were seeing
  the following offenses which were incorrect since we can't combine
  attrs that follow on from typed ones.
- This commit ensures that sibling accessors are groupable before
  raising an offense that they should be grouped.
- Also add more tests to ensure the offense detection and subsequent
  autocorrection still works.

```
  sig { returns(Pathname) }
  attr_reader :cached_location

  attr_reader :cache, :meta, :name, :version
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Group together all `attr_reader` attributes
```

changelog/fix_style_accessor_grouping_fix_sibling_detection_for.md

@@ -0,0 +1 @@
+* [#11675](https://github.com/rubocop/rubocop/pull/11675): `Style/AccessorGrouping`: Fix sibling detection for methods with type sigs. ([@issyl0][])

lib/rubocop/cop/style/accessor_grouping.rb

@@ -70,7 +70,7 @@ def on_class(node)
 
         def check(send_node)
           return if previous_line_comment?(send_node) || !groupable_accessor?(send_node)
-          return unless (grouped_style? && sibling_accessors(send_node).size > 1) ||
+          return unless (grouped_style? && groupable_sibling_accessors(send_node).size > 1) ||
                         (separated_style? && send_node.arguments.size > 1)
 
           message = message(send_node)
@@ -127,12 +127,12 @@ def separated_style?
           style == :separated
         end
 
-        def sibling_accessors(send_node)
+        def groupable_sibling_accessors(send_node)
           send_node.parent.each_child_node(:send).select do |sibling|
             sibling.attribute_accessor? &&
               sibling.method?(send_node.method_name) &&
               node_visibility(sibling) == node_visibility(send_node) &&
-              !previous_line_comment?(sibling)
+              groupable_accessor?(sibling) && !previous_line_comment?(sibling)
           end
         end
 
@@ -143,7 +143,7 @@ def message(send_node)
 
         def preferred_accessors(node)
           if grouped_style?
-            accessors = sibling_accessors(node)
+            accessors = groupable_sibling_accessors(node)
             group_accessors(node, accessors) if node.loc == accessors.first.loc
           else
             separate_accessors(node)

spec/rubocop/cop/style/accessor_grouping_spec.rb

@@ -141,6 +141,47 @@ class Foo
       RUBY
     end
 
+    it 'does not register an offense for grouped accessors below a typechecked accessor method' do
+      expect_no_offenses(<<~RUBY)
+        class Foo
+          extend T::Sig
+
+          sig { returns(Integer) }
+          attr_reader :one
+
+          attr_reader :two, :three
+        end
+      RUBY
+    end
+
+    it 'registers an offense for grouped accessors distinct from a typechecked accessor method' do
+      expect_offense(<<~RUBY)
+        class Foo
+          extend T::Sig
+
+          sig { returns(Integer) }
+          attr_reader :one
+
+          attr_reader :two, :three
+          ^^^^^^^^^^^^^^^^^^^^^^^^ Group together all `attr_reader` attributes.
+
+          attr_reader :four
+          ^^^^^^^^^^^^^^^^^ Group together all `attr_reader` attributes.
+        end
+      RUBY
+
+      expect_correction(<<~RUBY)
+        class Foo
+          extend T::Sig
+
+          sig { returns(Integer) }
+          attr_reader :one
+
+          attr_reader :two, :three, :four
+        end
+      RUBY
+    end
+
     it 'registers an offense for accessors with method definitions' do
       expect_offense(<<~RUBY)
         class Foo