There's a merged pull request on the void-packages repository

gdm: enable smooth transition with plymouth.
https://github.com/void-linux/void-packages/pull/28570

Description:
Support for smooth transition was disabled years ago, when `plymouth` wasn't in the Void repo. `gdm` checks whether `plymouth` can be pinged at run time so that no hard dependency is required.

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#### General
- [ ] This is a new package and it conforms to the [quality requirements](https://github.com/void-linux/void-packages/blob/master/Manual.md#quality-requirements)

#### Have the results of the proposed changes been tested?
- [x] I use the packages affected by the proposed changes on a regular basis and confirm this PR works for me
- [ ] I generally don't use the affected packages but briefly tested this PR

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