fix test can_reload_model

[frank-dong-ms-zz]

Fix below test failure by increase wait time:

https://dev.azure.com/dnceng/public/_build/results?buildId=716174&view=logs&j=41509eb4-74ce-5e57-61b4-bdf74b39e7c1&t=522d178a-829f-5bff-ccb9-04bea054b64d

error message is like:

X Microsoft.Extensions.ML.FileLoaderTests.can_reload_model [2s 11ms]
Error Message:
FileLoader ChangeToken didn't fire before the allotted time.

this failure is tracked at #5266

[harishsk]

[codecov]

Codecov Report

Merging #5287 into master will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #5287   +/-   ##
=======================================
  Coverage   73.68%   73.68%           
=======================================
  Files        1022     1022           
  Lines      190320   190320           
  Branches    20470    20470           
=======================================
+ Hits       140232   140237    +5     
+ Misses      44557    44555    -2     
+ Partials     5531     5528    -3     

Flag	Coverage Δ
#Debug	73.68% <ø> (+<0.01%)	⬆️
#production	69.42% <ø> (+<0.01%)	⬆️
#test	87.62% <ø> (ø)

Impacted Files	Coverage Δ
...c/Microsoft.ML.FastTree/Utils/ThreadTaskManager.cs	79.48% <0.00%> (-20.52%)	⬇️
...StandardTrainers/Standard/LinearModelParameters.cs	66.58% <0.00%> (+0.25%)	⬆️
...soft.ML.Data/DataLoadSave/Text/TextLoaderCursor.cs	89.45% <0.00%> (+0.47%)	⬆️
...rosoft.ML.AutoML/ColumnInference/TextFileSample.cs	65.56% <0.00%> (+5.96%)	⬆️