Add nightly-6.3 to Swift SDK for Android version matrix

Linux Docker images for 6.3 development snapshots are not available yet and will be added in a separate change.

Author: MaxDesiatov

.github/workflows/main.yml

@@ -242,6 +242,7 @@ jobs:
       matrix:
         include:
           - swift-version: "6.2"
+          - swift-version: "nightly-6.3"
           - swift-version: nightly-main
 
     steps: