[IMP] web: removed extra space in export field list

before this commit:
when manually adding field in export wizard, string has extra space in
begining.

after this commit:
manually added field in export field list doesn't contain any extra
spaces.

task-2065433

closes odoo/odoo#36759

Signed-off-by: Xavier Morel (xmo) <xmo@odoo.com>

addons/web/static/src/js/widgets/data_export.js

@@ -139,7 +139,7 @@ var DataExport = Dialog.extend({
             $fieldList.append(
                 $('<li>', {'class': 'o_export_field', 'data-field_id': fieldID}).append(
                     $('<span>', {'class': "fa fa-arrows o_short_field mx-1"}),
-                    label,
+                    label.trim(),
                     $('<span>', {'class': 'fa fa-trash m-1 pull-right o_remove_field', 'title': _t("Remove field")})
                 )
             );

addons/web/static/tests/widgets/data_export_tests.js

@@ -212,7 +212,7 @@ QUnit.module('widgets', {
     });
 
     QUnit.test('Export dialog UI test', async function (assert) {
-        assert.expect(4);
+        assert.expect(5);
         var list = await createView({
             View: ListView,
             model: 'partner',
@@ -269,6 +269,8 @@ QUnit.module('widgets', {
         // Add field
         await testUtils.dom.click($('.modal div:contains(Activities) .o_add_field'));
         assert.strictEqual($('.modal .o_fields_list li').length, 2, "There should be two fields in export field list.");
+        assert.strictEqual($('.modal .o_fields_list li:eq(1)').text(), "Activities",
+            "string of second field in export list should be 'Activities'");
         // Remove field
         await testUtils.dom.click($('.modal .o_fields_list li:first .o_remove_field'));
         assert.strictEqual($('.modal .o_fields_list li').length, 1, "There should be only one field in list");