R#: Set extension block to warning severity

[bkoelman]

Repro for https://youtrack.jetbrains.com/issue/RSRP-502336

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.21%. Comparing base (4dc5d8b) to head (d7ebe76).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1860   +/-   ##
=======================================
  Coverage   92.21%   92.21%           
=======================================
  Files         437      437           
  Lines       14866    14866           
  Branches     2451     2451           
=======================================
  Hits        13708    13708           
  Misses        713      713           
  Partials      445      445           

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