PYTHON-5656: Fixes broken link to aggregation pipeline docs. (#2627)

(cherry picked from commit 8bf8263)

Author: caseyclements

pymongo/asynchronous/database.py

@@ -701,7 +701,7 @@ async def aggregate(
         .. versionadded:: 3.9
 
         .. _aggregation pipeline:
-            https://mongodb.com/docs/manual/reference/operator/aggregation-pipeline
+            https://www.mongodb.com/docs/manual/core/aggregation-pipeline/
 
         .. _aggregate command:
             https://mongodb.com/docs/manual/reference/command/aggregate

pymongo/synchronous/database.py

@@ -701,7 +701,7 @@ def aggregate(
         .. versionadded:: 3.9
 
         .. _aggregation pipeline:
-            https://mongodb.com/docs/manual/reference/operator/aggregation-pipeline
+            https://www.mongodb.com/docs/manual/core/aggregation-pipeline/
 
         .. _aggregate command:
             https://mongodb.com/docs/manual/reference/command/aggregate