fix: add missing type annotations and remove unused variables in new tests

Pyright flagged three inner class `status` methods missing a type
annotation on the `quiet` parameter, and two unused variables
(`written`, `real_status`) left over from an earlier draft of
test_docker_quiet_true_suppresses_stderr.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/unit/test_backend_selection.py

@@ -409,7 +409,7 @@ class TestIsBackendReady(unittest.TestCase):
 
     def test_ready_when_status_returns_zero(self):
         class _ReadyBackend:
-            def status(self, *, quiet=False):
+            def status(self, *, quiet: bool = False) -> int:
                 return 0
 
         from bot_bottle.backend import is_backend_ready
@@ -418,7 +418,7 @@ class TestIsBackendReady(unittest.TestCase):
 
     def test_not_ready_when_status_nonzero(self):
         class _BrokenBackend:
-            def status(self, *, quiet=False):
+            def status(self, *, quiet: bool = False) -> int:
                 return 1
 
         from bot_bottle.backend import is_backend_ready
@@ -429,7 +429,7 @@ class TestIsBackendReady(unittest.TestCase):
         calls = []
 
         class _SpyBackend:
-            def status(self, *, quiet=False):
+            def status(self, *, quiet: bool = False) -> int:
                 calls.append(quiet)
                 return 0