test-backend: Update blacklist of covered files based on CI.

After accidentally merging ecadb33fbc
before I go CI input, I discovered that coverage in my development
environment differs from that in CI :(.

tools/test-backend

@@ -69,6 +69,7 @@ not_yet_fully_covered = {
     'zerver/lib/events.py',
     'zerver/lib/bugdown/__init__.py',
     'zerver/lib/events.py',
+    'zerver/lib/i18n.py',
     'zerver/lib/integrations.py',
     'zerver/lib/message.py',
     'zerver/lib/narrow.py',
@@ -104,6 +105,8 @@ not_yet_fully_covered = {
     'zerver/views/home.py',
     'zerver/views/registration.py',
     'zerver/views/events_register.py',
+    # This one has 1 line that isn't covered in Python 3
+    'zerver/views/upload.py',
     # Getting this to 100% is a major project goal.
     'zproject/backends.py',
 }