fitBounds() with `around` and `linear = true` don't fit given bounds.

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**mapbox-gl-js version**: 2.4.1

**browser**: Chrome 94.0.4606.71

### Steps to Trigger Behavior

1. Create a map
2. Call `fitBounds()` with `around` set to target bounds center and `linear: true` .
3. Call `fitBounds()` a second time to fit different bounds, again with `around` set to target bounds center.

Note : `around` is set up to target bounds center as I don't want to zoom around the map absolute center but straight to target bounds.

### Link to Demonstration

https://jsfiddle.net/qmartouzet/5frts3w8/

I've set up different bounds and buttons corresponding which `fitBounds()` to those. This allows to play and observe various behaviour.

### Expected Behavior

The map fits the given bounds.

### Actual Behavior

The map fits apparently random area. It's worth noting that result area seems consistent across multiple run.

**EDIT :** Turns out, as I was looking for a workaround, that padding isn't involved in this bug. When I use `around` option set to target bounds center, successive call to `fitBounds()` produces erratic results.

**EDIT 2 :** I forgot to mention that option `linear: true` needs to be set to produce this bug.

Start by reproducing the successive fitBounds() calls from the linked JSFiddle with around set to each target bounds center and linear: true. Trace the fitBounds() entry point and related camera transition behavior; done means repeated calls fit the requested bounds rather than producing an erratic area.

Written by the indexing model from the issue text.