BUG: insert styles from StyleManager with !important broken

### Reproducible demo link

https://jsfiddle.net/q7cxvpf5/1/

### Describe the bug

When I use this code it stops working after one div change and then no longer accepts any more style changes to any other divs:
editor.on('styleable:change', (model, property) => {
        const value = model.getStyle()[property];
        if (value.indexOf('!important') === -1) {
          model.addStyle({ [property]: value + ' !important' });
        }
});

When I use this code it inserts thousands of !importants and breaks the style:

editor.on('styleable:change', (model, property) => {
      const value = model.getStyle()[property];
      console.log('Styled ', property, value);
      if (styleImportant) {
        model.addStyle({ [property]: value + ` !important` });
      }
    });

These are the only two solutions I have been able to find in the project discussions.

If you have one that works, please let me know, or fix the bug.

### Code of Conduct

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