Fixed errcheck issues in server/channels/app/session_test.go (#29198)

server/.golangci.yml

@@ -138,7 +138,6 @@ issues:
         channels/app/security_update_check.go|\
         channels/app/server.go|\
         channels/app/server_test.go|\
-        channels/app/session_test.go|\
         channels/app/slack.go|\
         channels/app/slashcommands/auto_environment.go|\
         channels/app/slashcommands/command_loadtest.go|\