in CrossValidationReporter plots neg_RMSE is not negative

[MarieS-WiMLDS]

Describe the bug

Steps/Code to Reproduce

import skore 
project = skore.create("my_project", overwrite = True)
from sklearn.datasets import make_regression
X, y = make_regression(n_samples=500, n_features=7, noise=1, random_state=1)
from sklearn.ensemble import HistGradientBoostingRegressor
reg = HistGradientBoostingRegressor()
cv_reporter_reg = skore.CrossValidationReporter(reg, X, y, cv=10)
project.put("cv_regression", cv_reporter_reg)

Expected Behavior

if the value if positive, the name shouldn't start with neg.

Actual Behavior

Neg.

Environment

System:
    python: 3.12.8 | packaged by Anaconda, Inc. | (main, Dec 11 2024, 16:31:09) [GCC 11.2.0]
executable: /home/marie/anaconda3/envs/skore_test/bin/python
   machine: Linux-6.8.0-49-generic-x86_64-with-glibc2.35

Python dependencies:
        skore: 0.0.0+unknown
          pip: 24.2
   setuptools: 75.1.0
    diskcache: 5.6.3
      fastapi: 0.115.6
        numpy: 2.2.0
 plotly<6,>=5: None
      pyarrow: 18.1.0
         rich: 13.9.4
scikit-learn<1.7: None
        skops: 0.11.0
      uvicorn: 0.32.1

[glemaitre]

It should be fixed in #1009 as well.