Fix breadcrumb sorting when using `structlog-sentry`

[antonpirker]

How do you use Sentry?

Sentry Saas (sentry.io)

Version

2.11.0

Steps to Reproduce

There is a problem with the new breadcrumb sorting in combination with structlog as described here: kiwicom/structlog-sentry#159

The problem was intruduced here: #3307

Expected Result

Sort even if datetime is a string

Actual Result

crash

[antonpirker]

Closing in favor of: #3508