Bug 35212: Correct mismatched label on identity provider entry form

Bug 35212: Correct mismatched label on identity provider entry form

This patch corrects the identity provider form so that the label for the
"Allow staff" field has the correct "for" attribute. Currently it is a
duplicate of the one for the "Allow OPAC" field.

To test, apply the patch and go to Administration -> Identity providers.

- Click "New identity provider"
- Near the bottom of the form, look for the "Allow staff" field.
- Clicking the "Allow staff" label should activate the corresponding
  dropdown.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>