fix: correct the case sensitivity behavior for PromQL

[waynexia]

I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

Use TableReference::bare to avoid unnecessary escaping or parsing

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.

Refer to a related PR or issue link (optional)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6b4be3a) 85.50% compared to head (582246b) 85.08%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3296      +/-   ##
==========================================
- Coverage   85.50%   85.08%   -0.43%     
==========================================
  Files         872      872              
  Lines      141719   141721       +2     
==========================================
- Hits       121174   120579     -595     
- Misses      20545    21142     +597