Proposed changes

Prior to these changes, whenever it runs, the built-in bridge produces two warnings like this:

2025-10-15T13:40:55.752977Z  WARN MQTT bridge: [local] Received ack for unknown pkid=2

This is caused by the healthcheck message, which we ignore in the ack processing as we don't need to forward the acknowledgement to the other broker like we do for forwarded messages. Since this case isn't actually the bridge or broker misbehaving, this PR prevents the bridge warning when it receives the ack for the healthcheck message.

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (general improvements like code refactoring that doesn't explicitly fix a bug or add any new functionality)
• Documentation Update (if none of the other choices apply)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Paste Link to the issue

Checklist

• I have read the CONTRIBUTING doc
• I have signed the CLA (in all commits with git commit -s. You can activate automatic signing by running just prepare-dev once)
• I ran just format as mentioned in CODING_GUIDELINES
• I used just check as mentioned in CODING_GUIDELINES
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments