Disable singlehtml for releases until fixed

Summary

The single HTML documentation is not working on all machines including the one to create the release. This issue covers not building with --singlehtml for releases until the issue can be resolved.

Steps to reproduce

The failing environment is:

1. FreeBSD 14.1
2. Python 3.9 or 3.22
3. Package install npm-node18, npm-node20 or npm-node22. All fail.
4. NPM install inliner using npm install -g inliner

The failure is the generated HTML file is empty. If the commands are run manually a suitable HTML is created.