docker: install libgtk-4-1 needed by playwright

[tdesveaux]

eg. https://buildbot.buildbot.net/#/builders/122/builds/4820/steps/8/logs/stdio

L554

╔══════════════════════════════════════════════════════╗
║ Host system is missing dependencies to run browsers. ║
║ Please install them with the following command:      ║
║                                                      ║
║     sudo yarn playwright install-deps                ║
║                                                      ║
║ Alternatively, use apt:                              ║
║     sudo apt-get install libgtk-4-1                  ║
║                                                      ║
║ <3 Playwright Team                                   ║
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