[SQL Lab] Fixed TableElement sorting functionality and tests (#7069)

[enricoberti]

Also updated the test to get the first col from the mock table

[codecov-io]

Codecov Report

Merging #7070 into master will increase coverage by <.01%.
The diff coverage is 87.5%.

@@            Coverage Diff             @@
##           master    #7070      +/-   ##
==========================================
+ Coverage   64.46%   64.47%   +<.01%     
==========================================
  Files         421      421              
  Lines       20537    20544       +7     
  Branches     2247     2249       +2     
==========================================
+ Hits        13240    13246       +6     
- Misses       7170     7171       +1     
  Partials      127      127

Impacted Files	Coverage Δ
...rset/assets/src/SqlLab/components/TableElement.jsx	89.18% <87.5%> (-0.37%)	⬇️

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[mistercrunch]

This indeterministic test has been bugging me every now and then. LGTM