Fix compiler warning on typedef redeclaration

Fix compiler warning on typedef redeclaration

    bulk_write.c:78:3: error: redefinition of typedef 'BulkWriteState' is a C11 feature [-Werror,-Wtypedef-redefinition]
    } BulkWriteState;
      ^
    ../../../../src/include/storage/bulk_write.h:20:31: note: previous definition is here
    typedef struct BulkWriteState BulkWriteState;
                                  ^
    1 error generated.

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