Server error - Failed to start Lemmy

[hermann-san]

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Describe the bug

Starting Lemmy after installation fails.

Context

• Hardware: VPS bought online / Old laptop or computer / Raspberry Pi at home / Internet Cube with VPN / Other ARM board / ...
• YunoHost version: 11.2.30.2 (stable)
• I have access to my server: Through SSH | through the webadmin | direct access via keyboard / screen | ...
• Are you in a special context or did you perform some particular tweaking on your YunoHost instance?: *no
• Using, or trying to install package version/branch:

Steps to reproduce

1. install Lemmy
2. Open the Lemmy URL

Expected behavior

A clear and concise description of what you expected to happen. You can remove this section if the command above is enough to understand your intent.

Logs

Browser

Error!
There was a server error. Try reloading the website. If that doesn't work, come back later

YH Admin - Services logs

Sep 22 00:45:14 systemd[1]: lemmy.service: Main process exited, code=exited, status=101/n/a
Sep 22 00:45:14 systemd[1]: lemmy.service: Failed with result 'exit-code'.
Sep 22 00:45:14 systemd[1]: lemmy.service: Scheduled restart job, restart counter is at 5.
Sep 22 00:45:14 systemd[1]: Stopped Lemmy: Link aggregator.
Sep 22 00:45:14 systemd[1]: lemmy.service: Start request repeated too quickly.
Sep 22 00:45:14 systemd[1]: lemmy.service: Failed with result 'exit-code'.
Sep 22 00:45:14 systemd[1]: Failed to start Lemmy: Link aggregator.

thread 'main' panicked at 'Couldn't run DB Migrations: Failed to run 2022-07-07-182650_comment_ltrees with: permission denied to create extension "ltree"', crates/db_schema/src/utils.rs:221:25
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

It looks like there is an issue with Postgres databases that are already installed on the YH server. I currently have Postgres 13 installed and Lemmy doesn't seem to like that according to this issue.
LemmyNet/lemmy#3756
Installing on a YH server that doesn't have already a Postgres server installed is working fine.

I don't know if there is a solution to this available, but if not, it would be good to warn YH users before the installation.