fix: Use github.sha instead of hashFiles in container workflow

Replace hashFiles('**/Package.resolved') with github.sha for cache key
as hashFiles doesn't work properly in Docker container environment.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: fatbobman

.github/workflows/linux-compatibility.yml

@@ -28,7 +28,7 @@ jobs:
         path: |
           .build
           ~/.cache/org.swift.swiftpm
-        key: ${{ runner.os }}-swift-6.0-${{ hashFiles('**/Package.resolved') }}
+        key: ${{ runner.os }}-swift-6.0-${{ github.sha }}
         restore-keys: |
           ${{ runner.os }}-swift-6.0-
           ${{ runner.os }}-swift-