Why does cirq produce a non-positive semidefinite density matrix doing quantum tomography?

Question

While doing quantum tomography in cirq, I ended up getting a density matrix which is not positive semi-definite. Why is this so? Here's the code I used:

import cirq
from cirq.experiments import state_tomography
q0, q1, q2 = cirq.LineQubit.range(3)
circuit = cirq.Circuit(
    cirq.CNOT(q0,q1),         
    cirq.CNOT(q0, q2)    
)
simulator = cirq.Simulator()
results = state_tomography(
    sampler=simulator,
    qubits=[q0, q1],
    circuit=circuit,
    repetitions=5000
)
density_matrix = results.data
print("Reconstructed Density Matrix:")
print(density_matrix)
eigenvalues, _ = np.linalg.eigh(density_matrix)
print(eigenvalues)