CI against release ver of ptvsd, allow failure of master ver of ptvsd

[DonJayamanne]

Fixes #1253

This pull request:

• Has a title summarizes what is changing
• Includes a news entry file (remember to thank yourself!)
• Has unit tests & code coverage is not adversely affected (within reason)
• Works on all actively maintained versions of Python (e.g. Python 2.7 & the latest Python 3 release)
• Works on Windows 10, macOS, and Linux (e.g. considered file system case-sensitivity)

[codecov]

Codecov Report

Merging #1408 into master will decrease coverage by 0.3%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1408      +/-   ##
==========================================
- Coverage   71.31%   71.01%   -0.31%     
==========================================
  Files         271      271              
  Lines       12529    12529              
  Branches     2228     2228              
==========================================
- Hits         8935     8897      -38     
- Misses       3457     3499      +42     
+ Partials      137      133       -4

Impacted Files	Coverage Δ
src/client/linters/errorHandlers/notInstalled.ts	33.33% <0%> (-61.12%)	⬇️
src/client/linters/errorHandlers/errorHandler.ts	77.77% <0%> (-22.23%)	⬇️
src/client/common/logger.ts	53.33% <0%> (-20.01%)	⬇️
src/client/common/application/applicationShell.ts	23.07% <0%> (-7.7%)	⬇️
...lient/debugger/DebugServers/RemoteDebugServerv2.ts	67.85% <0%> (-7.15%)	⬇️
src/client/common/installer/productInstaller.ts	60.31% <0%> (-6.88%)	⬇️
src/client/linters/baseLinter.ts	87.5% <0%> (-4.17%)	⬇️
src/client/debugger/mainV2.ts	78.62% <0%> (-1.62%)	⬇️
...rc/client/debugger/PythonProcessCallbackHandler.ts	53.61% <0%> (+0.65%)	⬆️
src/client/linters/lintingEngine.ts	91.22% <0%> (+0.87%)	⬆️

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