Screen lock should not prevent volume controls from working

[hackerb9]

Describe the bug
Volume down and mute do not work when workrave is taking a break.

To Reproduce
Steps to reproduce the behavior:

1. In Preferences → Timers, uncheck Show Postpone and Show Skip buttons
2. In Preferences → UI, set Block Mode to "Input and Screen"
3. Take a break with workrave
4. Press the 🔉─ (volume down) key on the keyboard and notice it does nothing. Same for 🔇 (mute)

Expected behavior
I expected workrave to not capture the media control keys. Or, if it had to catch them all, then to pass on critical keys like Mute as faked key events to the window manager (XTEST). Failing that, I expected Workrave would handle the audio level itself.

Linux (please complete the following information in case you encountered the bug on Linux):

• Distribution: Debian
• Distribution Version: 1.10.52-3
• Desktop Environment: Gnome 46.4 (X11)
• Workrave Version: 1.10.52

Additional context

I found that I got in the habit of mindlessly dismissing workrave without thinking so I set it up to not show Postpone or Skip.

Approximately thirty seconds ago I clicked a web link right as workrave locked my screen. An extraordinarily loud commercial began playing and I found it rather frustrating that trying to make it stop only caused workrave to pause the timer countdown.