Sometimes: Fontconfig warning / Failed to connect to socket when running BackstopJS 6.0.4 in a docker container

This error occurs sporadically, e.g. in two of 26 test runs
```log
URL > ...
BROWSER: > HeadlessChrome/97.0.4691.0
COMMAND | Command "test" ended with an error after [46.821s]
COMMAND | Error: Failed to launch the browser process!
Fontconfig warning: "/etc/fonts/fonts.conf", line 100: unknown element "blank"
[0126/024642.946354:ERROR:bus.cc(397)] Failed to connect to the bus: Failed to connect to socket /var/run/dbus/system_bus_socket: No such file or directory
Inconsistency detected by ld.so: ../elf/dl-tls.c: 493: _dl_allocate_tls_init: Assertion `listp->slotinfo[cnt].gen <= GL(dl_tls_generation)' failed!

TROUBLESHOOTING: https://github.com/puppeteer/puppeteer/blob/main/docs/troubleshooting.md

at onClose (/usr/local/lib/node_modules/backstopjs/node_modules/puppeteer/lib/cjs/puppeteer/node/BrowserRunner.js:229:20)
at ChildProcess. (/usr/local/lib/node_modules/backstopjs/node_modules/puppeteer/lib/cjs/puppeteer/node/BrowserRunner.js:220:79)
at ChildProcess.emit (events.js:387:35)
at Process.ChildProcess._handle.onexit (internal/child_process.js:277:12)
```
Docker Version 20.10.12
Ubuntu Version 20.04.3 LTS