Fix cache eviction for ratelimit objects

discord/http.py

@@ -335,6 +335,7 @@ class Ratelimit:
         'reset_after',
         'expires',
         'dirty',
+        '_last_request',
         '_max_ratelimit_timeout',
         '_loop',
         '_pending_requests',
@@ -355,6 +356,7 @@ class Ratelimit:
         # The object that is sleeping is ultimately responsible for freeing the semaphore
         # for the requests currently pending.
         self._sleeping: asyncio.Lock = asyncio.Lock()
+        self._last_request: float = self._loop.time()
 
     def __repr__(self) -> str:
         return (
@@ -422,7 +424,12 @@ class Ratelimit:
     def is_expired(self) -> bool:
         return self.expires is not None and self._loop.time() > self.expires
 
+    def is_inactive(self) -> bool:
+        delta = self._loop.time() - self._last_request
+        return delta >= 300 and self.outgoing == 0 and len(self._pending_requests) == 0
+
     async def acquire(self) -> None:
+        self._last_request = self._loop.time()
         if self.is_expired():
             self.reset()
 
@@ -532,7 +539,7 @@ class HTTPClient:
         if len(self._buckets) < 256:
             return
 
-        keys = [key for key, bucket in self._buckets.items() if bucket.is_expired()]
+        keys = [key for key, bucket in self._buckets.items() if bucket.is_inactive()]
         for key in keys:
             del self._buckets[key]