Do not request the same log line from Registry on every iteration

[fsoikin]

Description of the change

Turns out the Registry understands the since field as "greater or equal", so that sending the last line's timestamp on the next request results in returning that same last line again.

To fix, I'm adding a millisecond to the timestamp, so that the same line doesn't qualify anymore.

Another option could be to patch the registry to change the meaning of the since field to just "greater". But since milliseconds are integer anyway, 1 is the smallest difference, so the result would be the same.

I tested the change manually by publishing a package. But there is no automated test. Turns out, there are no tests for non-offline publishing at all. Adding them would require mocking the Registry API, and I didn't think it was warranted for such small and largely insignificant change.

Fixes #1381

Checklist:

• Added the change to the "Unreleased" section of the changelog
• Added some example of the new feature to the README
• Added a test for the contribution (if applicable)

P.S.: the above checks are not compulsory to get a change merged, so you may skip them. However, taking care of them will result in less work for the maintainers and will be much appreciated 😊

[fsoikin]

I'm not entirely sure why the Windows test is failing. I didn't even change anything there.