chore(deps): update etherpad/etherpad docker tag to v1.9.4

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
etherpad/etherpad	final	patch	1.9.3 -> 1.9.4

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Release Notes

ether/etherpad-lite (etherpad/etherpad)

v1.9.4

Compare Source

Compability changes

• Log4js has been updated to the latest version. As it involved a bump of 6 major version.
  A lot has changed since then. Most notably the console appender has been deprecated. You can find out more about it here

Notable enhancements and fixes

• Fix for MySQL: The logger calls were incorrectly configured leading to a crash when e.g. somebody uses a different encoding than standard MySQL encoding.

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