[easy][PyTorchEdge] Add magic number to flatbuffer schema (#74048)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/74048
ghstack-source-id: 151064703
Test Plan:
```
Executing in directory: /data/users/pavithran/fbsource
buck build //xplat/caffe2:mobile_bytecode --config client.id=nuclide
DEBUG: /data/users/pavithran/fbsource/tools/build_defs/fbcode_macros/build_defs/lib/cpp_common.bzl:287:14: Using disallowed linker flag 'ANativeActivity_onCreate' in library rule 'fbsource//third-party/toolchains/android-ndk:r18b_native_app_glue'
Parsing buck files: finished in 1.2 sec
Building: finished in 0.4 sec (100%) 1/1 jobs, 1/1 updated
Total time: 1.7 sec
More details at https://www.internalfb.com/intern/buck/build/ad0db098-e3c1-465c-b69a-3cda4ab9c2ee
BUILD SUCCEEDED
```
Reviewed By: dbort
Differential Revision: D34797167
fbshipit-source-id: f3c115f80951bb11e17163283603aa7877c7c472
(cherry picked from commit 2ded6963c5d57b6c1e5ff15b8fa3b7d81e66bb33)
