Make logging to Cloud more robust in the face of a bad log

[cicdw]

Thanks for contributing to Prefect!

Please describe your work and make sure your PR:

• adds new tests (if appropriate)
• updates CHANGELOG.md (if appropriate)
• updates docstrings for any new functions or function arguments, including docs/outline.toml for API reference docs (if appropriate)

Note that your PR will not be reviewed unless all three boxes are checked.

What does this PR change?

This PR ensures that a single bad non-JSON serializable log doesn't prevent further logs from arriving in Cloud.

Why is this PR important?

A user was attempting to log bytes from a subprocess, and all logs stopped arriving in Cloud (because bytes aren't JSON serializable). This is undesirable behavior, and as many logs as possible should be getting through.

[codecov]

Codecov Report

Merging #1845 into master will increase coverage by 0.02%.
The diff coverage is 100%.

[codecov]

Codecov Report

Merging #1845 into master will increase coverage by 0.02%.
The diff coverage is 100%.