fix: another typo in prepare_operator!!

[lkdvos]

Fixes #425

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
.../algorithms/derivatives/hamiltonian_derivatives.jl	0.00%	1 Missing ⚠️

Files with missing lines	Coverage Δ
.../algorithms/derivatives/hamiltonian_derivatives.jl	93.13% <0.00%> (ø)

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