Guard instrumentation exclude Interlocked

[ViktorHofer]

Excluding System.Threading.Interlocked from instrumentation which is used for recording hits. Not excluding that type would cause an infinite loop as it would call itself.

cc @sharwell @tonerdo

[codecov]

Codecov Report

Merging #302 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #302      +/-   ##
==========================================
+ Coverage   89.06%   89.08%   +0.01%     
==========================================
  Files          16       16              
  Lines        1912     1915       +3     
==========================================
+ Hits         1703     1706       +3     
  Misses        209      209

Impacted Files	Coverage Δ
src/coverlet.core/Instrumentation/Instrumenter.cs	99.05% <100%> (ø)	⬆️

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[ViktorHofer]

@tonerdo it would be great if we could release a new package with this change and #276 to unblock us in corefx and dotnet/machinelearning.