[C++] Flatbuffer binary fails to verify alignment for int64 in a vector of tables

[ghkinoo]

While attempting to update to the latest flatbuffers library (v24.12.23), some of our serialized buffers started to fail verification. In particular they couldn't verify the alignment of an int64 field in a table that's within a vector. I reproduced the issue here: https://github.com/ghkinoo/test_flatbuffer

The gist of it though:

table TestTable {
    test_id: string;
    test_long: long;
}

table TestRoot {
    tests: [TestTable];
}

{
  "tests": [
    {
      "test_id": "test1",
      "test_long": 8569750533
    }
  ]
}

test_long doesn't align to 8 in the subsequent binary, as far as the verifier is concerned at least.

This may be related to this #8397