Update libddwaf gem to v1.15.0.0.0

Gemfile

@@ -90,9 +90,3 @@ end
 group :dev do
   gem 'ruby-lsp', require: false if RUBY_VERSION >= '3.0.0' && RUBY_PLATFORM != 'java'
 end
-
-# `1.17.0` provides broken RBS type definitions
-# https://github.com/ffi/ffi/blob/master/CHANGELOG.md#1170rc1--2024-04-08
-#
-# TODO: Remove this once the issue is resolved: https://github.com/ffi/ffi/issues/1107
-gem 'ffi', '~> 1.16.3', require: false

Steepfile

@@ -552,7 +552,6 @@ target :datadog do
 
   repo_path 'vendor/rbs'
   library 'cucumber'
-  library 'ffi'
   library 'jruby'
   library 'gem'
   library 'rails'
@@ -575,7 +574,8 @@ target :datadog do
   library 'graphql'
   library 'datadog-ci'
 
-  # TODO: gem 'libddwaf'
-  library 'libddwaf'
+  # ffi version 1.17 was shipped with invalid rbs types:
+  # https://github.com/ffi/ffi/issues/1107
+  library 'libddwaf-stub'
   library 'libdatadog'
 end

datadog.gemspec

@@ -65,7 +65,7 @@ Gem::Specification.new do |spec|
   spec.add_dependency 'datadog-ruby_core_source', '~> 3.3'
 
   # Used by appsec
-  spec.add_dependency 'libddwaf', '~> 1.14.0.0.0'
+  spec.add_dependency 'libddwaf', '~> 1.15.0.0.0'
 
   # When updating the version here, please also update the version in `libdatadog_extconf_helpers.rb`
   # (and yes we have a test for it)