Do not report anonymous block arguments in Lint/UnusedArgument

spec/ameba/rule/lint/unused_argument_spec.cr

@@ -132,6 +132,15 @@ module Ameba::Rule::Lint
       subject.catch(s).should_not be_valid
     end
 
+    it "doesn't report if it's an anonymous block" do
+      s = Source.new %(
+        def method(&)
+          yield 1
+        end
+      )
+      subject.catch(s).should be_valid
+    end
+
     it "doesn't report if variable is referenced implicitly" do
       s = Source.new %(
         class Bar < Foo

src/ameba/ast/variabling/argument.cr

@@ -31,7 +31,12 @@ module Ameba::AST
     def initialize(@node, @variable)
     end
 
-    # Returns `true` if the name starts with '_', `false` if not.
+    # Returns `true` if the `name` is empty, `false` otherwise.
+    def anonymous?
+      name.blank?
+    end
+
+    # Returns `true` if the `name` starts with '_', `false` otherwise.
     def ignored?
       name.starts_with? '_'
     end

src/ameba/rule/lint/unused_argument.cr

@@ -55,7 +55,8 @@ module Ameba::Rule::Lint
 
     private def find_unused_arguments(source, scope)
       scope.arguments.each do |argument|
-        next if argument.ignored? || scope.references?(argument.variable)
+        next if argument.anonymous? || argument.ignored?
+        next if scope.references?(argument.variable)
 
         name_suggestion = scope.node.is_a?(Crystal::Block) ? '_' : "_#{argument.name}"
         issue_for argument.node, MSG % {argument.name, name_suggestion}