CI fix: drop forward-ref quotes from iter_accessible_slots annotation

ruff UP037: `list[tuple[int, "ItemSlot | None"]]` -> the quotes were
unnecessary because `ItemSlot` is imported at the module top (line 52)
and `from __future__ import annotations` is in effect. Plain
`list[tuple[int, ItemSlot | None]]` is the canonical form.

Verification:
* ruff check python/minecraft_bot tests: all checks passed.
* pytest tests/python/unit: 980 passed.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: AlexMelanFromRingo

python/minecraft_bot/bot.py

@@ -833,7 +833,7 @@ def count_item(self, name: str) -> int:
         """Total count of items named ``name`` across the inventory."""
         return self.inventory.count_item(name)
 
-    def iter_accessible_slots(self) -> list[tuple[int, "ItemSlot | None"]]:
+    def iter_accessible_slots(self) -> list[tuple[int, ItemSlot | None]]:
         """All visible slots — player_slots followed by container_slots.
 
         Use this for operations that genuinely need the merged view