fix: mysql writer does not print error message in some cases

[evenyag]

I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

This PR fixes the issue that our MySQL handler may not print the error message to users.

It outputs OK but the query actually fails if the error is an internal error.

Query OK (0.02 sec)

Now users can see the internal error message.

ERROR 1815 (HY000): Internal error: 1003

Checklist

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.

Refer to a related PR or issue link (optional)

[v0y4g3r]

LGTM

[codecov]

Codecov Report

Merging #2763 (e93d014) into develop (d2cf72e) will decrease coverage by 0.41%.
Report is 2 commits behind head on develop.
The diff coverage is 16.66%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2763      +/-   ##
===========================================
- Coverage    85.38%   84.97%   -0.41%     
===========================================
  Files          774      774              
  Lines       125811   125936     +125     
===========================================
- Hits        107419   107018     -401     
- Misses       18392    18918     +526