misc: fix creation of inspect_url for link to parent form (#41662)

tests/test_backoffice_pages.py

@@ -6141,6 +6141,10 @@ def test_backoffice_create_carddata_from_formdata(pub, studio):
     resp = resp.form.submit(name='button_createcard').follow()
     assert 'Card nr. 1-1 created' in resp
 
+    # visit inspect page
+    resp = app.get(formdata.get_url(backoffice=True) + 'inspect')
+    assert "variables from parent's request" in resp
+
 
 def test_backoffice_after_submit_location(pub):
     create_superuser(pub)

wcs/backoffice/management.py

@@ -2666,7 +2666,7 @@ class FormBackOfficeStatusPage(FormStatusPage):
                 r += htmltext('  <div class="value"><span>%(caption)s '
                               '(<a href="%(inspect_url)s">%(display_name)s)</a></span>') % {
                     'caption': htmltext('<var>%s</var>') % _('variables from parent\'s request'),
-                    'inspect_url': v['form'].backoffice_url() + 'inspect',
+                    'inspect_url': v['form'].backoffice_url + 'inspect',
                     'display_name': v['form_display_name'],
                 }
             elif hasattr(v, 'inspect_keys') or isinstance(v, dict):