notify-send does not notify and hangs on master

Output of `awesome --version`:

```
awesome v4.3-314-g1116bc47 (Too long)
• Compiled against Lua 5.3.5 (running with Lua 5.3)
• D-Bus support: ✔
• xcb-errors support: ✘
• execinfo support: ✔
• xcb-randr version: 1.6
• LGI version: 0.9.2
```
**How to reproduce the issue:**

- Use awesome master
- `notify-send "anything"`

**Actual result:**

- No notification is shown
- notify-send hangs and never exits

**Expected result:**

- Notification should be shown

Ping: @Elv13

Reproduce the issue on awesome master by running `notify-send "anything"` and confirm that no notification appears and the command hangs. Trace the notification path involved in this behavior; done means a notification is shown and `notify-send` exits normally.

Written by the indexing model from the issue text.