Fix repository reference in Notebook

[dtulga]

Just a quick fix to rename the repository reference from dvcx to datachain in this notebook.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.50%. Comparing base (ed98e4b) to head (fed9c3c).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #105      +/-   ##
==========================================
- Coverage   85.62%   85.50%   -0.12%     
==========================================
  Files          93       92       -1     
  Lines        9459     9197     -262     
  Branches     1887     1499     -388     
==========================================
- Hits         8099     7864     -235     
+ Misses       1031     1012      -19     
+ Partials      329      321       -8     

Flag	Coverage Δ
datachain	85.50% <ø> (-0.06%)	⬇️

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