[wasm coreclr] wrong fields alignment

the runtime initialization is failing with

```
Assert failure(PID 42 [0x0000002a], Thread: 1263252 [0x134694]): Consistency check failed: Managed object size does not match unmanaged object size
man: 0x2c, unman: 0x30, Name: System.Runtime.Loader.AssemblyLoadContext

FAILED: size == expectedsize
    File: /Users/rodo/git/runtime-main/src/coreclr/vm/binder.cpp:660
    Image: /managed
```
