tests/unit: Use password of length 6

As we changed the minimal length we need to have passwords of that length (even for the tests)
3 jobs for feature-s/1682-allow-user-to-modify-password in 6 minutes and 18 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Test Tools
passed #416969
test_tools

00:00:07

 
  Test Unit
passed #416970
web
test_server_unit

00:00:16

 
  Test Functional
passed #416971
docker x86_64
test_server_functional

00:05:55