fix: add required pubkey for 1.25.5

Roman's key is necessary to build for nginx 1.25.5.

You can verify the key is legitimate through:

wget https://nginx.org/download/nginx-1.25.5.tar.gz
wget https://nginx.org/download/nginx-1.25.5.tar.gz.asc
gpg --verify nginx-1.25.5.tar.gz.asc

Before creating a PR, run through this checklist and mark each as complete.

[x] I have written my commit messages in the Conventional Commits format.
[x] I have read the CONTRIBUTING doc
[x] I have added tests (when possible) that prove my fix is effective or that my feature works
[x] I have checked that all unit tests pass after adding my changes
[x] I have updated necessary documentation
[x] I have rebased my branch onto master
[x] I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

nginxinc / ngx-rust