Improve the icon of the 'remove from inbox' action

### Checklist

- [X] I have used the search function for [**OPEN**](https://github.com/AntennaPod/AntennaPod/issues) issues to see if someone else has already submitted the same feature request.
- [X] I have **also** used the search function for [**CLOSED**](https://github.com/AntennaPod/AntennaPod/issues?q=is%3Aissue+is%3Aclosed) issues to see if the feature was already implemented and is just waiting to be released, or if the feature was rejected.
- [X] I will describe the problem with as much detail as possible.
- [X] This request contains only one single feature, **not** a list of multiple (related) features.

### App version

3.4.1

### Where did you get the app from

Google Play

### Feature or improvement you want

Change the icon of the 'remove from inbox' icon to something more descriptive than the checkbox.

### Why should this be added?

> Having had a look at the swipe icons they all seem pretty obvious and/or standard. The one exception is using a simple tick “✓” for “Remove from inbox” as I don’t think this is obvious. Perhaps some thought could be given to an icon that more accurately reflects this action? Something like an inbox tray with a cross or a minus sign on it perhaps? Or maybe with a tick on it as that is more in line with the mindset of processing an inbox?

https://forum.antennapod.org/t/write-out-swipe-actions/4503/7

### Screenshots / Drawings / Technical details


> with something like this as the basis - sorry not good at manipulatng images.