**Steps to reproduce:**
* Install the **Netherlands - SBR** (`l10n_nl_reports_sbr`) and **Netherlands - SBR OB Nummer** (`l10n_nl_reports_sbr_ob_nummer`) modules.
* Create two companies with Dutch localization.
* Go to **Accounting → Configuration → Tax Units** and create a Tax Unit with its own **Tax ID** (e.g. `NL826317558B01`), adding both companies.
* On the main company form, fill in the **Omzetbelastingnummer** field (e.g. `123456782B90`).
* Go to **Accounting → Reporting → Tax Return**, select the Tax Unit in the filter, and click **XBRL → Download XBRL File**.

**Observed behavior:**
* The `<xbrli:identifier>` in the exported XBRL file contains the company's **Omzetbelastingnummer** (`123456782B90`) instead of the Tax Unit's VAT (`826317558B01`).
* The tax authority rejects the return because the identifier does not match the fiscal unity registration.

**Cause:**
* `_get_sbr_identifier()` in `l10n_nl_reports_sbr_ob_nummer` unconditionally returns `self.env.company.l10n_nl_reports_sbr_ob_nummer` before consulting the Tax Unit.
* The `super()` call, which correctly routes to `tax_unit.vat` via `report.get_vat_for_export()`, is only reached when the company field is empty — so the Tax Unit's VAT is never used when a company OB-number is set.

**Fix:**
* When a Tax Unit is active in the report options, delegate immediately to `super()._get_sbr_identifier()`, which resolves `tax_unit.vat` through the existing `get_vat_for_export()` logic.
* The company-level `l10n_nl_reports_sbr_ob_nummer` override is preserved as a fallback for the `company_only` (no Tax Unit) case.

opw-6350840

Forward-Port-Of: odoo/enterprise#125167