fix(fabric.Canvas): set isMoving on real movement only

[asturur]

close #5378
Set the isMoving boolean only on real movement more than on mousemove event.

[github-actions]

Code Coverage Summary

> fabric@4.3.1 coverage:report /home/runner/work/fabric.js/fabric.js
> nyc report --reporter=lcov --reporter=text

-----------|---------|----------|---------|---------|-----------------------------------------------
File       | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s                             
-----------|---------|----------|---------|---------|-----------------------------------------------
All files  |    82.7 |    76.91 |    85.6 |   82.46 |                                               
 fabric.js |    82.7 |    76.91 |    85.6 |   82.46 | ...,29558,29683,29763-29828,29951,30050,30267 
-----------|---------|----------|---------|---------|-----------------------------------------------