Title is bold, but label is not. What to do?

I made a small reproducible program, where you will see the title in bold font, but the label in normal font:

import matplotlib.pyplot as plt
import seaborn as sns
import numpy as np

observed = np.array([28, 15, 21, 23, 17, 22, 19, 19, 24, 27, 20, 21, 25, 25, 16, 20, 23])

fig, ax = plt.subplots(figsize=(4, 2))

sns.histplot(ax = ax, x = list(observed), label = "observed data") 
ax.set_title("Observed data", fontweight='bold')

ax.legend()
plt.show()

I tried to set the label in bold by putting the same code fontweight='bold' (after the label = term) inside the sns.histplot instruction, but this leads to an error:

sns.histplot(ax = ax, x = list(observed), label = "observed data", fontweight='bold') 

Okay, I admit that it wasn't a very smart attempt, but I don't know how to get the label in bold, in a simple way... Could someone help me to do so?

Adjust the font properties of the legend:

ax.legend(prop={"weight": "bold"})

https://matplotlib.org/3.5.0/api/_as_gen/matplotlib.pyplot.legend.html