Add missing include header (#5721)

https://github.com/triton-lang/triton/pull/5542/files introduced a
dependency on an unordered_map without requiring the unordered_map
include path.

This works on some systems currently if other headers include unordered
map, but fails on others.

Author: wsmoses

include/triton/Dialect/TritonGPU/IR/Dialect.h

@@ -11,6 +11,8 @@
 #include "triton/Dialect/TritonGPU/IR/Attributes.h"
 #include "triton/Dialect/TritonGPU/IR/Types.h"
 
+#include <unordered_map>
+
 // LinearLayoutCache Utils
 using CacheKey =
     std::tuple<std::vector<int64_t>, mlir::Attribute, std::optional<int32_t>>;