api/throttling: Fix mypy errors after djangorestframework-stubs update
15:40:17 mypy run-test-pre: PYTHONHASHSEED='1405704389'
15:40:17 mypy run-test: commands[0] | mypy swh
15:40:29 swh/web/api/throttling.py:141: error: Cannot determine type of 'num_requests'
15:40:29 swh/web/api/throttling.py:142: error: Cannot determine type of 'num_requests'
15:40:29 Found 2 errors in 1 file (checked 155 source files)
Migrated from D4390 (view on Phabricator)