Bump mop version to 3.1.0-SNAPSHOT

[streamnativebot]

This is a PR created by snbot to trigger the check suite in each repository.

[github-actions[bot]]

@streamnativebot:Thanks for your contribution. For this PR, do we need to update docs? (The PR template contains info about doc, which helps others know more about the changes. Can you provide doc-related info in this and future PR descriptions? Thanks)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 77.17%. Comparing base (05f43d6) to head (6dc1779).

Additional details and impacted files

@@               Coverage Diff                @@
##             branch-3.1    #1288      +/-   ##
================================================
+ Coverage         77.06%   77.17%   +0.11%     
- Complexity         1011     1013       +2     
================================================
  Files               111      111              
  Lines              4451     4451              
  Branches            354      354              
================================================
+ Hits               3430     3435       +5     
+ Misses              823      820       -3     
+ Partials            198      196       -2     

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