Switch to HEAD of Chrono 0.4.x

[umanwizard]

This has two benefits:

1. We will no longer risk calling the old, buggy from_timestamp_millis function (which had the property that NaiveDateTime::from_timestamp_millis(-1000) did not compare equal to NaiveDateTime::from_timestamp_opt(-1, 0). It has been fixed in the latest Chrono.
2. We will be able to use the from_timestamp_micros function introduced in Add from_timestamp_micros function chronotope/chrono#906 , rather than duplicating this error-prone logic in our own codebase.

Once Chrono does another release of 0.4.x, we can stop depending on HEAD.

Motivation

See initial section

Tips for reviewer

Checklist

• This PR has adequate test coverage / QA involvement has been duly considered.

• This PR evolves an existing $T ⇔ Proto$T mapping (possibly in a backwards-incompatible way) and therefore is tagged with a T-proto label.

• This PR includes the following user-facing behavior changes:

• None

[benesch]

Thanks! Fixed the missing comma in deny.toml and marked for automerge.