fix: memory leak in unit test of telemetry

[waynexia]

I hereby agree to the terms of the GreptimeDB CLA.

Refer to a related PR or issue link (optional)

What's changed and what's your intention?

Remove this:

let url = Box::leak(format!("{}:{}", "http://localhost", port).into_boxed_str());

Checklist

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
• This PR does not require documentation updates.

[evenyag]

......

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.69%. Comparing base (b8a325d) to head (31e11c2).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3897      +/-   ##
==========================================
- Coverage   86.03%   85.69%   -0.35%     
==========================================
  Files         955      955              
  Lines      163851   163870      +19     
==========================================
- Hits       140969   140427     -542     
- Misses      22882    23443     +561