ci: Explicitly build just the winit package on Android

Since rust-mobile/cargo-subcommand#23 `cargo-apk`
now strictly searches for workspaces first before committing to finding
the right package _within said workspace_, and bails when no package was
selected since we don't support selecting (building, packaging, running)
>1 target currently.

Perhaps it's a bit hash to enforce this on free-form `cargo apk --`
invocations, but it is what it is.

.github/workflows/ci.yml

@@ -33,7 +33,7 @@ jobs:
           - { target: x86_64-unknown-linux-gnu, os: ubuntu-latest,   }
           - { target: x86_64-unknown-linux-gnu, os: ubuntu-latest, options: --no-default-features, features: x11 }
           - { target: x86_64-unknown-linux-gnu, os: ubuntu-latest, options: --no-default-features, features: "wayland,wayland-dlopen" }
-          - { target: aarch64-linux-android,    os: ubuntu-latest,  cmd: 'apk --', features: "android-native-activity" }
+          - { target: aarch64-linux-android,    os: ubuntu-latest, options: -p winit, cmd: 'apk --', features: "android-native-activity" }
           - { target: x86_64-apple-darwin,      os: macos-latest,    }
           - { target: x86_64-apple-ios,         os: macos-latest,    }
           - { target: aarch64-apple-ios,        os: macos-latest,    }