Bar Chart: doesn't respect axis placement for same units

### What happened? The bar chart panel appears to ignore assigning a field to a different axis if the units are not also changed, but the legend still has the `right y-axis` suffix: <img width="868" height="386" alt="Image" src="https://github.com/user-attachments/assets/037cb827-ae0e-4332-a9cc-8dbbb861cbaf" /> Similar fix for time series panel: https://github.com/grafana/grafana/pull/41635/ I did a hack here https://github.com/lukester1975/grafana/commit/0f4bd97ee403335c8556161dc160c26f0c60bcd1 that looks better, but I'm sure there are other things to consider beyond my ken for a proper fix... ### What did you expect to happen? With my hack: <img width="868" height="386" alt="Image" src="https://github.com/user-attachments/assets/0ef391ae-3634-4a3a-83e7-6b96840076ee" /> ### Did this work before? I don't believe so. ### How do we reproduce it? 1. Plot a couple of fields in a bar chart 2. Add a field override to a bar chart for axis placement on the right for a field 3. No secondary y-axis will appear, unless the field override also changes the units to differ from the other field(s) ### Is the bug inside a dashboard panel? _No response_ ### Environment (with versions)? Grafana: 12.4 OS: Linux Browser: Firefox ### Grafana platform? Other ### Datasource(s)? _No response_