docs(table): fix table async example backend sort function

[dauriata]

Proposed Changes

Fixes Table async data example when using the table sorting function
Using wrong property in sort function

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 17.86%. Comparing base (484cfe8) to head (5a09018).
Report is 57 commits behind head on develop.

Files	Patch %	Lines
...oruga/src/components/table/examples/async-data.vue	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           develop     #910       +/-   ##
============================================
- Coverage    56.71%   17.86%   -38.86%     
============================================
  Files           30      292      +262     
  Lines         1511     7317     +5806     
  Branches       544     2093     +1549     
============================================
+ Hits           857     1307      +450     
- Misses         654     5059     +4405     
- Partials         0      951      +951     

Flag	Coverage Δ
oruga-next	17.86% <0.00%> (-38.86%)	⬇️

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