Allow String in task_namespace

Author: sue445

_gem/lib/go_gem/rake_task.rb

@@ -34,7 +34,7 @@ class RakeTask < ::Rake::TaskLib
     attr_reader :gem_name
 
     # @!attribute task_namespace
-    #   @return [Symbol] task namespace (default: `:go`)
+    #   @return [Symbol,String] task namespace (default: `:go`)
     attr_accessor :task_namespace
 
     # @!attribute go_bin_path

_gem/sig/go_gem/rake_task.rbs

@@ -2,7 +2,7 @@ module GoGem
   class RakeTask < ::Rake::TaskLib
     @gem_name: String
 
-    @task_namespace: Symbol
+    @task_namespace: Symbol | String
 
     @go_bin_path: String
 
@@ -18,7 +18,7 @@ module GoGem
 
     attr_reader gem_name: String
 
-    attr_accessor task_namespace: Symbol
+    attr_accessor task_namespace: Symbol | String
 
     attr_accessor go_bin_path: String