• #553: Fix logging to include the full traceback when Borg experiences an internal error, not just
  the first few lines.
• #554: Fix all monitoring hooks to warn if the server returns an HTTP 4xx error. This can happen
  with Healthchecks, for instance, when using an invalid ping URL.
• #555: Fix environment variable plumbing so options like "encryption_passphrase" and
  "encryption_passcommand" in one configuration file aren't used for other configuration files.

From 1.6.4:

• #546, #382: Keep your repository passphrases and database passwords outside of borgmatic's
  configuration file with environment variable interpolation. See the documentation for more
  information: https://torsion.org/borgmatic/docs/how-to/provide-your-passwords/