Prevent remote-change events from occurring in push-only mode

[7hong13]

What this PR does / why we need it?

In pushOnly mode, a remote-change event can be triggered unexpectedly. This issue occurs when switching from pushPull mode to pushOnly mode before receiving a response to the sync (pushPull) request.
This PR fixes the issue to prevent remote change events from occurring in pushOnly mode.

Any background context you want to provide?

What are the relevant tickets?

• Prevent remote-change events from occurring in push-only mode yorkie-js-sdk#759
• Remote-change event occurs in PushOnly mode yorkie-js-sdk#758

Fixes #

Checklist

• Added relevant tests or not required
• Didn't break anything

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.64%. Comparing base (79f4573) to head (acac530).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #161      +/-   ##
==========================================
+ Coverage   79.63%   79.64%   +0.01%     
==========================================
  Files          63       63              
  Lines        3855     3857       +2     
  Branches      606      606              
==========================================
+ Hits         3070     3072       +2     
  Misses        459      459              
  Partials      326      326              

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