.gitignore and .gitlab-ci.yml templates for C++ don't work

Summary

.gitignore template for C++ doesn't work

Steps to reproduce

1. create new file in UI
2. choose .gitignore or .gitlab-ci.yml
3. from the list of templates choose c++

What is the current bug behavior?

just showing loading indicator and nothing happens

What is the expected correct behavior?

it should paste prepared text from the template to file

Relevant logs and/or screenshots

Output of checks

This bug happens on GitLab.com too

Results of GitLab environment info

Tested on own self-hosted version and on gitlab.com

/label ~bug /duplicate #52942 (closed)