`var"LogMessage.Level"` is deprecated

[MilesCranmer]

Seeing this warning during precompilation, just an FYI:

┌ TensorBoardLogger
│  ┌ Warning: `var"LogMessage.Level"` is deprecated.
│  │   caller = ip:0x0
│  └ @ Core :-1
│  ┌ Warning: `LogMessage` is deprecated.
│  │   caller = ip:0x0
│  └ @ Core :-1
└

[oxinabox]

I am guessing this is an easy fix, but it is a matter of finding time

[rossviljoen]

This is causing precompilation to fail on Julia Version 1.12.0-rc1:

ERROR: LoadError: FieldError: type Core.TypeName has no field 'mt'

https://github.com/JuliaLogging/TensorBoardLogger.jl/blame/a5a9205ff06d6fb6a83e26028f1168eeb1c3ab16/src/protojl/tensorboard/tensorboard/event_pb.jl#L145

[MilesCranmer]

#148 just need someone with merge rights