Fix: progress bar for merge_datasets

[bhimrazy]

Before submitting

• Was this discussed/agreed via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?

What does this PR do?

Fixes #433

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79%. Comparing base (04e77c0) to head (f9910e5).
Report is 1 commits behind head on main.

Additional details and impacted files

@@         Coverage Diff         @@
##           main   #445   +/-   ##
===================================
  Coverage    79%    79%           
===================================
  Files        35     35           
  Lines      5102   5104    +2     
===================================
+ Hits       4006   4008    +2     
  Misses     1096   1096