Change staff importers to accept xlsx (#1703)

evap/evaluation/tests/test_misc.py

evap/staff/fixtures/excel_files_test_data.py

evap/staff/fixtures/invalid_user_import.xls

evap/staff/fixtures/invalid_user_import.xlsx

evap/staff/fixtures/valid_user_import.xls

evap/staff/fixtures/valid_user_import.xlsx

evap/staff/forms.py

evap/staff/importers.py

evap/staff/templates/staff_evaluation_person_management.html

evap/staff/templates/staff_semester_import.html

evap/staff/templates/staff_user_import.html

evap/staff/tests/test_importers.py

evap/staff/tests/test_views.py

evap/staff/urls.py

evap/staff/views.py

evap/static/sample.xls

evap/static/sample.xlsx

evap/static/sample_user.xls

evap/static/sample_user.xlsx

pyproject.toml