Add build mode to Swift autobuild check

Author: henrymercer

.github/workflows/__swift-autobuild.yml

@@ -1,16 +1,13 @@
 name: "Swift analysis using autobuild"
 description: "Tests creation of a Swift database using autobuild"
-# versions: ["latest", "cached", "nightly-latest"]
 versions: ["nightly-latest"]
-# Swift autobuilder is only supported on MacOS for private beta
 operatingSystems: ["macos"]
-env:
-  CODEQL_ENABLE_EXPERIMENTAL_FEATURES_SWIFT: "true" # Remove when Swift is GA.
 steps:
   - uses: ./../action/init
     id: init
     with:
       languages: swift
+      build-mode: autobuild
       tools: ${{ steps.prepare-test.outputs.tools-url }}
   - uses: ./../action/.github/actions/setup-swift
     with: