fix(testnet): listen_addr default deserialization

[oxarbitrage]

Motivation

Resolve a small bug report. Fixes #6386

Solution

• Changed deserialization to 0.0.0.0 as suggested.
• Tested manually, bug is gone.
• All tests pass locally.
• Need to see if the CI pass.

Review

Anyone can review.

Reviewer Checklist

• Will the PR name make sense to users?
  • Does it need extra CHANGELOG info? (new features, breaking changes, large changes)
• Are the PR labels correct?
• Does the code do what the ticket and PR says?
  • Does it change concurrent code, unsafe code, or consensus rules?
• How do you know it works? Does it have tests?

Follow Up Work

[codecov]

Codecov Report

Merging #6575 (1708264) into main (a1b3246) will decrease coverage by 0.03%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6575      +/-   ##
==========================================
- Coverage   77.76%   77.74%   -0.03%     
==========================================
  Files         307      307              
  Lines       40287    40287              
==========================================
- Hits        31331    31322       -9     
- Misses       8956     8965       +9