Fontconfig warning: ignoring en-US LC_CTYPE en_US.UTF-8: not a valid language tag

**Describe the bug**
The warning appears when sending a subscription email when an instance spins up, after the first email, it doesn't appear anymore

**Logs**
NA

**To Reproduce**
1) set up Metabase via a Docker container (w/ maildev as well), build a question and add it to a dashboard
2) send the dashboard as a subscription and check the logs

**Expected behavior**
No warning, in fact, if you run the plain JAR this doesn't happen

**Screenshots**
NA

**Information about your Metabase Installation:**
- Your browser and the version: Brave latest
- Your operating system: Ubuntu 20.04.4
- Your databases: Postgres 14.4
- Metabase version: 1.42.3
- Metabase hosting environment: Docker
- Metabase internal database: Postgres 14.4

**Severity**
Not severe

**Additional context**
Might be because of https://github.com/metabase/metabase/blob/a7bfefe0997f950e5f4d7ad93b035d4fc888a98a/bin/docker/Dockerfile#L3, but I don't know the impact of removing/changing that

Start with bin/docker/Dockerfile at the referenced line and compare the Docker container environment with the plain JAR setup. Reproduce the warning by sending a dashboard subscription, then determine whether the container locale configuration causes it; done means the warning no longer appears without affecting email delivery.

Written by the indexing model from the issue text.