test: add tests for drop databases

[WenyXu]

I hereby agree to the terms of the GreptimeDB CLA.

Refer to a related PR or issue link (optional)

#3516

What's changed and what's your intention?

add tests for drop databases

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.

[codecov]

Codecov Report

Attention: Patch coverage is 95.78059% with 20 lines in your changes are missing coverage. Please review.

Project coverage is 84.94%. Comparing base (623c930) to head (e9df15d).

❗ Current head e9df15d differs from pull request most recent head e4c21d7. Consider uploading reports for the commit e4c21d7 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3594      +/-   ##
==========================================
- Coverage   85.20%   84.94%   -0.26%     
==========================================
  Files         930      931       +1     
  Lines      154235   154702     +467     
==========================================
- Hits       131422   131418       -4     
- Misses      22813    23284     +471     

[fengjiachun]

LGTM