Upgrade Rust toolchain to nightly-2023-02-04

[tautschnig]

Description of changes:

Manually move the toolchain pointer by a single day (while we are waiting for automatic PRs to start working - see #2323).

Resolved issues:

n/a

Related RFC:

n/a

Call-outs:

n/a

Testing:

• How is this change tested? Will be tested in this PR.

• Is this a refactor change? No.

Checklist

• Each commit message has a non-empty body, explaining why the change was made
• n/a Methods or procedures are documented
• Regression or unit tests are included, or existing tests cover the modified code
• My PR is restricted to a single feature or bugfix

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.