CS:S fails to update the spray from an image in the filesystem

**Game information**

- Counter Strike: Source

**Distribution name and version where applicable**

Arch Linux

**Flatpak info**

```
$ flatpak --version
Flatpak 1.14.0
$ flatpak --gl-drivers
default
host
```

**Problem description**

When I try to replace the current spray with a new `.jpg` image, a small popup window appears, informing that it failed; then I see the message in the console:

```
WARN_FILEWRITE - Asked to write to '/home/user/temp0.tga', but we don't own that location. Disallowing.
```
**Does this issue reproduce with native Steam**

No