fix typo when setting Pr to default

[j-fu]

Prevents these warnings:

┌ Warning: cg! doesn't support right preconditioning. └ @ LinearSolve ~/.julia/packages/LinearSolve/fBayl/src/iterative_wrappers.jl:168

[vpuri3]

thanks for catching my mistake!

[codecov[bot]]

Codecov Report

Merging #272 (ff5a503) into main (c8e1358) will decrease coverage by 38.16%. The diff coverage is 100.00%.

@@             Coverage Diff             @@
##             main     #272       +/-   ##
===========================================
- Coverage   71.09%   32.93%   -38.16%     
===========================================
  Files          14       11        -3     
  Lines         858      759       -99     
===========================================
- Hits          610      250      -360     
- Misses        248      509      +261     

Impacted Files	Coverage Δ
src/iterative_wrappers.jl	53.96% <100.00%> (-23.36%)	:arrow_down:
src/factorization_sparse.jl	0.00% <0.00%> (-100.00%)	:arrow_down:
ext/LinearSolveHYPRE.jl	0.00% <0.00%> (-92.60%)	:arrow_down:
src/preconditioners.jl	21.42% <0.00%> (-58.58%)	:arrow_down:
src/factorization.jl	26.12% <0.00%> (-57.43%)	:arrow_down:
src/LinearSolve.jl	60.00% <0.00%> (-36.56%)	:arrow_down:
src/solve_function.jl	63.63% <0.00%> (-36.37%)	:arrow_down:
src/default.jl	32.53% <0.00%> (-21.69%)	:arrow_down:
src/common.jl	75.86% <0.00%> (-13.97%)	:arrow_down:
... and 3 more

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