[Bug]: PostgreSQL duplicate key value violates unique constraint "mimetype_id_index"

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github OR Nextcloud Community Forum (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

Hello,
on a fresh installation on Debian 12 with PostgreSQL I got: the following error in the postgresql.log:

025-07-29 22:16:33.439 UTC [26753] DBUSER@nextcloud ERROR:  duplicate key value violates unique constraint "mimetype_id_index"
2025-07-29 22:16:33.439 UTC [26753] DBUSER@nextcloud DETAIL:  Key (mimetype)=(image/svg+xml) already exists.
2025-07-29 22:16:33.439 UTC [26753] DBUSER@nextcloud STATEMENT:  INSERT INTO "oc_mimetypes" ("mimetype") VALUES($1)
2025-07-29 22:16:33.440 UTC [26757] DBUSER@nextcloud ERROR:  duplicate key value violates unique constraint "mimetype_id_index"
2025-07-29 22:16:33.440 UTC [26757] DBUSER@nextcloud DETAIL:  Key (mimetype)=(image/svg+xml) already exists.
2025-07-29 22:16:33.440 UTC [26757] DBUSER@nextcloud STATEMENT:  INSERT INTO "oc_mimetypes" ("mimetype") VALUES($1)

Steps to reproduce

1. Install Debian 12 in a LXC container
2. install all dependencies and nextcloud
3. configure postgresql
4. install + configure nextcloud

Expected behavior

No error messages in a fresh installation

Nextcloud Server version

31

Operating system

Debian 12

PHP engine version

8.2

Web server

Apache 2.4.62

Database engine version

PostgreSQL 15.13

Is this bug present after an update or on a fresh install?

yes

Are you using the Nextcloud Server Encryption module?

no

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

No repository file, test, or entry point is named. Reproduce the fresh Debian 12 installation with PostgreSQL 15.13, then trace the oc_mimetypes insertion that produces the duplicate image/svg+xml error. Done means a fresh Nextcloud 31 installation completes without duplicate-key errors and the relevant regression coverage passes.