Elixir 1.15 deprecates Logger.warn

[dustinfarris]

Our builds got a lot noisier with deprecation warnings from sentry after upgrading elixir. We also have to remove --warnings-as-errors in our CI for now.

https://github.com/elixir-lang/elixir/releases/tag/v1.15.0

4. Hard deprecations
[Logger] Logger.warn/2 is deprecated in favor of Logger.warning/2

[dustinfarris]

This is not Sentry-specific. Any custom logger backend is affected.

Fixed in elixir-lang/elixir#12698

It is incumbent on custom logger backends using the legacy API to translate :warn log-levels to :warning.