Relax verification on flat tensor (#15334)

This PR was created by the merge bot to help merge the original PR into
the main branch.
ghstack PR number: #15313 by
@lucylq
^ Please use this as the source of truth for the PR details, comments,
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ghstack PR base:
https://github.com/pytorch/executorch/tree/gh/lucylq/121/base
ghstack PR head:
https://github.com/pytorch/executorch/tree/gh/lucylq/121/head
Merge bot PR base: https://github.com/pytorch/executorch/tree/main
Merge bot PR head:
https://github.com/pytorch/executorch/tree/gh/lucylq/121/orig
Differential Revision:
[D85169688](https://our.internmc.facebook.com/intern/diff/D85169688/)
@diff-train-skip-merge

Co-authored-by: lucylq <[email protected]>

Author: pytorchbot

extension/flat_tensor/flat_tensor_data_map.cpp

@@ -218,7 +218,7 @@ ET_NODISCARD Result<const char*> FlatTensorDataMap::get_key(
   size_t expected_size = fh->segment_base_offset + fh->segment_data_size;
   size_t actual_size = loader->size().get();
   ET_CHECK_OR_RETURN_ERROR(
-      expected_size == actual_size,
+      expected_size <= actual_size,
       InvalidExternalData,
       "File size is too small; file may be corrupted or truncated. Expected %zu from flat_tensor header, received %zu from data loader",
       expected_size,