[Release 5.0] Fix async deadlock issue when sending attention fails due to network failure

[cheenamalhotra]

Ports #1766 to 5.0-servicing.

[codecov]

Codecov Report

Base: 65.47% // Head: 71.42% // Increases project coverage by +5.95% 🎉

Coverage data is based on head (f56719e) compared to base (914caf5).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@                Coverage Diff                @@
##           5.0-servicing    #1783      +/-   ##
=================================================
+ Coverage          65.47%   71.42%   +5.95%     
=================================================
  Files                293      293              
  Lines              61385    61385              
=================================================
+ Hits               40189    43843    +3654     
+ Misses             21196    17542    -3654     

Flag	Coverage Δ
addons	92.38% <ø> (+92.38%)	⬆️
netcore	75.01% <100.00%> (+5.81%)	⬆️
netfx	69.24% <100.00%> (+5.55%)	⬆️

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

Impacted Files	Coverage Δ
...c/Microsoft/Data/SqlClient/TdsParserStateObject.cs	81.65% <100.00%> (ø)
...c/Microsoft/Data/SqlClient/TdsParserStateObject.cs	81.79% <100.00%> (+0.21%)	⬆️
...re/src/Microsoft/Data/SqlClient/SNI/SNINpHandle.cs	73.77% <0.00%> (-4.92%)	⬇️
...rc/Microsoft/Data/ProviderBase/DbConnectionPool.cs	85.48% <0.00%> (-0.59%)	⬇️
...crosoft/Data/SqlClient/SqlInternalConnectionTds.cs	67.62% <0.00%> (+0.17%)	⬆️
...c/Microsoft/Data/SqlClient/SqlClientEventSource.cs	80.13% <0.00%> (+0.34%)	⬆️
...SqlClient/src/Microsoft/Data/SqlClient/SqlEnums.cs	77.37% <0.00%> (+0.63%)	⬆️
.../Data/SqlClient/SqlClientEventSource.NetCoreApp.cs	100.00% <0.00%> (+0.64%)	⬆️
...crosoft/Data/SqlClient/SqlInternalConnectionTds.cs	73.37% <0.00%> (+0.68%)	⬆️
... and 50 more

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