Assignment operator does not check for self-assignment

Defect 73571 (STATIC_C)
Checker SELF_ASSIGN (subcategory none)
File: /src/mongo/s/query/cluster_cursor_manager.cpp
Function mongo::ClusterCursorManager::PinnedCursor::operator =(mongo::ClusterCursorManager::PinnedCursor&&)
/src/mongo/s/query/cluster_cursor_manager.cpp, line: 101
No protection against the object assigning to itself.

        _manager = std::move(other._manager);