chore: bump version 0.6.8

[LucasXu0]

Feature Preview

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PR Checklist

• My code adheres to AppFlowy's Conventions
• I've listed at least one issue that this PR fixes in the description above.
• I've added a test(s) to validate changes in this PR, or this PR only contains semantic changes.
• All existing tests are passing.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.78%. Comparing base (c122f0a) to head (bca9e97).
Report is 267 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #6164       +/-   ##
===========================================
- Coverage   86.74%   74.78%   -11.97%     
===========================================
  Files         217      232       +15     
  Lines        5032     6242     +1210     
  Branches      831      990      +159     
===========================================
+ Hits         4365     4668      +303     
- Misses        561     1464      +903     
- Partials      106      110        +4     

Flag	Coverage Δ
appflowy_web_app	74.78% <ø> (-11.97%)	⬇️

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