fix: restrict main Ubuntu repos to amd64 for ARM64 cross-compilation

- Add [arch=amd64] restriction to main sources.list when building for ARM64
- Prevents 404 errors when apt tries to fetch arm64 packages from x86-only repos
- ARM64 packages correctly fetched only from ports.ubuntu.com
- x86_64 builds remain unaffected

Author: 123vivekr

.github/workflows/build-linux.yml

@@ -43,6 +43,9 @@ jobs:
             # Add ARM64 architecture
             sudo dpkg --add-architecture arm64
             
+            # Restrict main sources to amd64 only to prevent 404 errors
+            sudo sed -i 's/^deb /deb [arch=amd64] /g' /etc/apt/sources.list
+            
             # Add ARM64 repositories
             echo "deb [arch=arm64] http://ports.ubuntu.com/ubuntu-ports $(lsb_release -cs) main restricted universe multiverse" | sudo tee /etc/apt/sources.list.d/arm64.list
             echo "deb [arch=arm64] http://ports.ubuntu.com/ubuntu-ports $(lsb_release -cs)-updates main restricted universe multiverse" | sudo tee -a /etc/apt/sources.list.d/arm64.list