build script: Update SwiftPM preset

Update the mixin_swiftpm_package_(macos|linux)_platform presets include
Swift Testing and Swift Testing macros.

Author: bkhouri

utils/build-presets.ini

@@ -1887,6 +1887,8 @@ skip-test-swiftpm
 [preset: mixin_swiftpm_package_linux_platform]
 mixin-preset=mixin_swiftpm_linux_platform
 
+swift-testing
+swift-testing-macros
 skip-test-llbuild
 skip-test-swiftpm
 
@@ -1976,6 +1978,8 @@ mixin-preset=mixin_swiftpm_package_macos_platform
 release
 assertions
 swift-driver
+swift-testing
+swift-testing-macros
 
 [preset: buildbot_swift-driver_linux]
 mixin-preset=mixin_swiftpm_package_linux_platform