[Bug]: `radius` does not round the tray.

[Allusive]

Checklist

• I have read the appropriate section in the contributing guidelines
• I believe this issue is a problem with polybar itself and not a misconfiguration on my part
• I have searched for other open and closed issues that may have already reported this problem
• I have checked the known issues page for this problem.
• I have followed the debugging guide to narrow down the problem to a minimal config.

Steps to reproduce

Run polybar with config

Minimal config

radius = 10

tray-position = left

tray-detached = false

tray-maxsize = 16

tray-background = ${color.background}

tray-offset-x = 0
tray-offset-y = 0

tray-padding = 2

tray-scale = 1.0

### Polybar log

_No response_

### Expected behavior

Bar is rounded all the way round.

### Actual behavior

The rounding does not extend to the system tray.

### Window Manager and Version

XMonad 0.17.2

### Linux Distribution

NixOS 23.05

### Polybar version

```text
polybar 3.6.3

Features: +alsa +curl +i3 +mpd +network(libnl) +pulseaudio +xkeyboard

X extensions: +randr (+monitors) +composite +xkb +xrm +xcursor

Build type: Release
Compiler: /nix/store/lcf37pgp3rgww67v9x2990hbfwx96c1w-gcc-wrapper-12.2.0/bin/g++
Compiler flags:  -O3 -DNDEBUG -Wall -Wextra -Wpedantic -Wsuggest-override
Linker flags:  -Wall -Wextra -Wpedantic -Wsuggest-override  -Wall -Wextra -Wpedantic -Wsuggest-override

Additional Context / Screenshots

[Patrick Ziegler]

Duplicate of #651