Enable `block` variable in view

Remove `block` keyword from reserved method names

actionview/lib/action_view/template.rb

@@ -326,7 +326,7 @@ def handle_render_error(view, e) #:nodoc:
       def locals_code #:nodoc:
         # Only locals with valid variable names get set directly. Others will
         # still be available in local_assigns.
-        locals = @locals.to_set - Module::DELEGATION_RESERVED_METHOD_NAMES
+        locals = @locals.to_set - Module::DELEGATION_RESERVED_METHOD_NAMES.dup.delete("block")
         locals = locals.grep(/\A(?![A-Z0-9])(?:[[:alnum:]_]|[^\0-\177])+\z/)
 
         # Double assign to suppress the dreaded 'assigned but unused variable' warning

actionview/test/fixtures/test/test_template_with_block_variable.erb

+<%= block %>
\ No newline at end of file

actionview/test/template/compiled_templates_test.rb

@@ -14,6 +14,10 @@ def test_template_with_ruby_keyword_locals
       render(file: "test/render_file_with_ruby_keyword_locals", locals: { class: "foo" })
   end
 
+  def test_template_with_block_variable
+    assert_equal "foo", render(file: "test/test_template_with_block_variable", locals: { block: "foo" })
+  end
+
   def test_template_with_invalid_identifier_locals
     locals = {
       foo: "bar",