Add @types/sinon to unmock-core.

[ksaaskil]

• Quick fix while we think if we want to add all types as dependencies (Add types as dependencies. #201).
• Sinon definitely needs to be a dependency because we even export that

[codecov-io]

Codecov Report

Merging #203 into dev will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              dev     #203   +/-   ##
=======================================
  Coverage   88.81%   88.81%           
=======================================
  Files          48       48           
  Lines        1529     1529           
  Branches      357      357           
=======================================
  Hits         1358     1358           
  Misses        171      171

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