Make MlImage tests not block file for reading

[michaelgsharp]

Makes ML-Image tests not block the image file for reading as this is causing some test failures.

[michaelgsharp]

@tarekgh Is there a reason we make the image file on disk not be able to be read share opened?

[michaelgsharp]

/azp run

[azure-pipelines[bot]]

Azure Pipelines successfully started running 2 pipeline(s).

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 68.79%. Comparing base (d0aa2c2) to head (d6cbcdb).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7029   +/-   ##
=======================================
  Coverage   68.79%   68.79%           
=======================================
  Files        1254     1254           
  Lines      250204   250204           
  Branches    25529    25529           
=======================================
+ Hits       172127   172132    +5     
+ Misses      71467    71464    -3     
+ Partials     6610     6608    -2     

Flag	Coverage Δ
Debug	68.79% <100.00%> (+<0.01%)	:arrow_up:
production	63.22% <ø> (+<0.01%)	:arrow_up:
test	88.50% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
test/Microsoft.ML.Tests/ImagesTests.cs	91.79% <100.00%> (ø)

... and 2 files with indirect coverage changes