Fitting a line to 2 points with error in Python

Question

I am trying to just fit a line to 2 points that have errors on the y axis but I can't seem to get the uncertainty out of it. Here is my (very simple) code:

import numpy as np
from scipy.optimize import curve_fit

nu = np.array([0,1])
B = np.array([0.191989,0.19089])
err_B = np.array([5,50])*1e-5

def lin(x, a, b):
    return a-b*(x+1/2)

popt, pcov = curve_fit(lin, nu, B,sigma=err_B)
print(popt)
print(np.sqrt(np.diag(pcov)))

For the actual values I get what I expect, but for the errors I get inf. This is clearly wrong, as I can literally do error propagation and get the error on a and b by doing the calculations by hand. Can someone help me fix this issue and get the errors on the parameters? Thank you!