Use urlsafe base64 decode

lib/rails_ext/action_text_attachables.rb

@@ -20,7 +20,7 @@ ActiveSupport.on_load(:action_text_content) do
               # Rails 7 used an older format of GID that serialized the payload using Marshall
               # Since we intentionally skip signature verification, we can't safely unmarshal the data
               # To work around this, we manually extract the GID from the marshaled data
-              Base64.strict_decode64(data).match(%r{(gid://campfire/[^/]+/\d+)})&.to_s
+              Base64.urlsafe_decode64(data).match(%r{(gid://campfire/[^/]+/\d+)})&.to_s
             else
               nil
             end

test/lib/rails_ext/action_text_attachables_test.rb

@@ -15,7 +15,7 @@ class ActionText::AttachmentTest < ActiveSupport::TestCase
 
   test "from_node with a Rails 7 SGID" do
     gid = @user.to_gid.to_s
-    marshaled_gid = Base64.strict_encode64(Marshal.dump(gid))
+    marshaled_gid = Base64.urlsafe_encode64(Marshal.dump(gid))
     rails7_payload = { "_rails" => { "message" => marshaled_gid, "exp" => nil, "pur" => "attachable" } }
     rails7_message = Base64.strict_encode64(JSON.generate(rails7_payload))
     rails7_sgid = "#{rails7_message}--invalidsignature"