[19.0][FIX] queue_job: remove deprecated base.user_admin reference

[neoand]

Issue

`base.user_admin` was removed in Odoo 17+ (replaced by `base.group_system` + admin user via a separate ```). The xmlid is not available as a public reference in Odoo 17/18/19.

The current `security.xml` references it in `group_queue_job_manager.user_ids`:

```xml

```

This breaks `-u queue_job` on Odoo 17/18/19 with:

```
ValueError: External ID not found in the system: base.user_admin
while evaluating
"[Command.link(ref('base.user_root')), Command.link(ref('base.user_admin'))]"
```

Fix

Drop the second `Command.link`. Only `base.user_root` remains. Users (including admins) can still be added to the group via backoffice (Settings > Users & Companies > select user > Access Rights tab) or via a custom xmlid in a downstream module.

```diff
-
+
```

Reproduction

On any Odoo 17/18/19 deployment with `queue_job` 19.0.x installed:

```bash
odoo -d -u queue_job --stop-after-init --without-demo=all

ValueError: External ID not found in the system: base.user_admin

```

Related

The same bug exists in OCA/server-tools `auditlog` 19.0.x (`res_groups.xml`). A separate PR is needed there. Note that auditlog in the verbum fork has already been patched locally (commit 272d154 in neoand/verbum) to avoid the broken reference — happy to mirror that change here if OCA maintainers prefer a single-source approach.

Tested by

• Reproduced on Odoo 19.0-20260803 with queue_job 19.0.2.0.3
• After patch: `-u queue_job` succeeds; `group_queue_job_manager` is created correctly; admin user (`base.user_root`) is included automatically

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Hi @guewen, @sbidoul,
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