"bundle install" CA certificates

I am attempting to create a github pages website, and it requires me to do

bundle install

I have tried this, and this is the error message I'm getting:

Fetching source index from https://rubygems.org/
There is a chance you are experiencing a man-in-the-middle attack, but most likely your system doesn't have the CA certificates needed for verification. For information about OpenSSL certificates, see
https://railsapps.github.com/openssl-certificate-verify-failed.html. To connect without using SSL, edit your Gemfile sources and change 'https' to 'http'

I am wary of using 'http' to solve this issue. I have tried downloading the SSL cert file and have followed this guide, but unfortunately am unable to solve the issue: https://bundler.io/guides/rubygems_tls_ssl_troubleshooting_guide.html

These are the two commands I have run:

sudo cp ~/GlobalSignRootCA_R3.pem /usr/lib/ruby/vendor_ruby/rubygems/ssl_certs/rubygems.org
sudo cp ~/GlobalSignRootCA_R3.pem /usr/lib/ruby/3.0.0/rubygems/ssl_certs

Is there anything else I can do? I've looked at the other StackExchange posts, and it seems like this is an old but resolved issue, so I'm at a loss. I am using a Linux machine. Thank you!