What is the bug or the crash?

Within the graduated renderer panel, the 'legend format' is reset every time the classes are re-classified.

I believe this should not be the case. The 'legend format' should persist even after reclassification.

Steps to reproduce the issue

1. Create a new vector layer with a 'double' field, add a couple of features. For example:

l = QgsVectorLayer("LineString?field=test:double", "test layer", "memory")

f1=QgsFeature()
f1.setAttributes([1.0])

f2=QgsFeature()
f2.setAttributes([2.0])

with edit(l):
    l.addFeature(f1)
    l.addFeature(f2)
    
QgsProject().instance().addMapLayer(l)

2. Open the layer styling panel.

3. Set the layer styling to 'Graduated'

4. Set value to field of interest (with above examle it will be 'test')

5. Press 'Classify' -> all normal

6. Modify the 'Legend format' -> the labels update. All normal.

7. Press 'Classify' again -> the 'Legend format' is reset.

I believe that the 'Legend format' is not meant to be reset like this

Versions

Supported QGIS version

• I'm running a supported QGIS version according to the roadmap.

New profile

• I tried with a new QGIS profile

Additional context

No response