Enable Android build in CI (no tests, only build).

Enable the Android CI workflow added in swiftlang/github-workflows#172.

Author: grynspan

.github/workflows/pull_request.yml

@@ -24,6 +24,7 @@ jobs:
       enable_ios_checks: true
       ios_host_exclude_xcode_versions: '[{"xcode_version": "16.2"}, {"xcode_version": "16.3"}, {"xcode_version": "16.4"}]'
       enable_wasm_sdk_build: true
+      enable_android_sdk_build: true
   soundness:
     name: Soundness
     uses: swiftlang/github-workflows/.github/workflows/soundness.yml@main