TST: Relax tolerance for irf test on windows

[bashtage]

Relax tolerance on windows to avoid failure noise

• code/documentation is well formatted.
• properly formatted commit message. See
  NumPy's guide.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@d63cc96). Click here to learn what that means.
The diff coverage is 100%.

@@            Coverage Diff            @@
##             master    #5666   +/-   ##
=========================================
  Coverage          ?   82.15%           
=========================================
  Files             ?      593           
  Lines             ?    93546           
  Branches          ?    10340           
=========================================
  Hits              ?    76853           
  Misses            ?    14298           
  Partials          ?     2395

Impacted Files	Coverage Δ
statsmodels/tsa/vector_ar/tests/test_svar.py	100% <100%> (ø)

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