CI: Trigger the draft-release job only on tags

[ret2libc]

Your checklist for this pull request

• I've read the guidelines for contributing to this repository
• I made sure to follow the project's coding style
• [-] I've documented or updated the documentation of every function and struct this PR changes. If not so I've explained why.
• [-] I've added tests that prove my fix is effective or that my feature works (if possible)
• [-] I've updated the rizin book with the relevant information (if needed)

Detailed description

Fixes #4428

Test plan

• try it out in a fork
• check how new release process goes

Closing issues

Closes #4428

[XVilka]

LGTM if works. We should merge it before the next release