ci: use single commit on the deployment branch

[evenyag]

I hereby agree to the terms of the GreptimeDB CLA.

Refer to a related PR or issue link (optional)

• The repo is too large to clone due to the gh-pages branch #3579

What's changed and what's your intention?

This PR sets single-commit to true for the gh-pages branch. It should reduce the branch size.

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.

[tisonkun]

Thank you!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.89%. Comparing base (bf14d33) to head (5e810c7).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3580      +/-   ##
==========================================
- Coverage   85.25%   84.89%   -0.36%     
==========================================
  Files         917      917              
  Lines      152869   152869              
==========================================
- Hits       130324   129776     -548     
- Misses      22545    23093     +548