HTML preferences database: ensure lower-case mail addresses

Fix html preferences not being recognised if the mail address contains
upper-case characters: ensure the address is stored in lower-case.

Signed-off-by: Albrecht Dreß <albrecht.dress@netcologne.de>
1 job for imap-improvements in 1 minute and 9 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
failed #1308296
allowed to fail
code_quality

00:01:09

 
Name Stage Failure
failed
code_quality Test
$ function propagate_env_vars() { # collapsed multi-line command
$ docker pull --quiet "$CODE_QUALITY_IMAGE"
error during connect: Post http://docker:2375/v1.40/images/create?fromImage=registry.gitlab.com%2Fgitlab-org%2Fci-cd%2Fcodequality&tag=0.85.23: dial tcp: lookup docker on 192.168.122.1:53: no such host
Uploading artifacts for failed job
Uploading artifacts...
WARNING: gl-code-quality-report.json: no matching files
ERROR: No files to upload
Cleaning up file based variables
ERROR: Job failed: exit code 1