[torch][JIT] Warn only once when using unscripted dictionary (#59287)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/59287
D27211605 added a warning in `toIValue` that warns users to script their
dictionaries before passing them to TorchScript functions in order to get some
performance benefits and reference semantics. However, this warning is emitted
every time `toIValue` is called (e.g. when a dictionary is passed to
TorchScript function), which can lead to noisy log output. This diff changes
this changes to use `TORCH_WARN_ONCE` instead.
Test Plan: Sandcastle, OSS CI.
Reviewed By: hyuen
Differential Revision: D28824468
fbshipit-source-id: e651eade4380abaf77c6c8a81ec4e565b0c2c714
