Update docs for polar() keyword argument, it is alg (not algorithm)

[jaakkor2]

As coded here
https://github.com/JuliaLinearAlgebra/MatrixFactorizations.jl/blob/v3.0.1/src/polar.jl#L572-L573

function polar(A::AbstractMatrix{T};
                   alg::Symbol=:newton,

also tests are written with keyword alg, not algorithm.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.64%. Comparing base (6874396) to head (ec767d9).

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #70   +/-   ##
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  Coverage   92.64%   92.64%           
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  Files           9        9           
  Lines        1401     1401           
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  Hits         1298     1298           
  Misses        103      103           

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