[FIX] base: Allow user to change its own language

Before this change, it was not possible to a user to change its own
language via the Preference view.

In order to allow a user who does not have access rights on the
res.users model to modify his language (field included in the list of
SELF_WRITEABLE_FIELDS fields) it is necessary to force the reandly
attribute to False in the view used to edit the user's preferences.

opw-2151630
Closes #41412

closes odoo/odoo#41748

X-original-commit: 272bff9e3173e1ed5da5d5a87e4c7be53ad59700
Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>

odoo/addons/base/views/res_users_views.xml

@@ -354,7 +354,7 @@
                         <group>
                             <label for="lang"/>
                             <div class="o_row">
-                                <field name="lang"/>
+                                <field name="lang" readonly="0"/>
                                 <button
                                     type="action"
                                     name="%(base.res_lang_act_window)d"