fix typo in sparse SBP operators

[codecov[bot]]

Codecov Report

Merging #124 (ccab5ca) into main (5cf1f0d) will not change coverage. The diff coverage is 0.00%.

@@           Coverage Diff           @@
##             main     #124   +/-   ##
=======================================
  Coverage   96.23%   96.23%           
=======================================
  Files          25       25           
  Lines        2841     2841           
=======================================
  Hits         2734     2734           
  Misses        107      107           

Impacted Files	Coverage Δ
src/RefElemData_SBP.jl	81.12% <0.00%> (ø)

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[jlchan]

Windows test failures appear to be spurious...