"Generating..." leaves artifacts in debug output

[MinchinWeb]

A spinner was added post 4.6 (which is snazzy!), but it leaves an artifact on the following debug lines. Ideally these lines would be overwritten rather than appended.

• I have read the Filing Issues and subsequent “How to Get Help” sections of the documentation.
• I have searched the issues (including closed ones) and believe that this is not a duplicate.

• OS version and name: Windows 10
• Python version: 3.9.6
• Pelican version: master at e800b23 (post 4.6)
• Link to theme:
• Links to plugins:
• Link to your site:
• Link to your source: not yet on GitHub
• Link to a Gist with the contents of your settings file:

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your participation and understanding.

[MinchinWeb]

Waiting on #2897

[justinmayer]

Ostensibly addressed by #2897.