Fix SUPASS environment variable in docker-compose-dl-streamer-example

[rawatts10]

Change from SUPASS to SUPASS=${SUPASS} to properly pass through the environment variable.

📝 Description

Adding additional environment variables after this line can be problematic since the SUPASS wasn't set to any value. This fix correctly sets the SUPASS to the host environment variable for SUPASS (if used).

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• [ x ] 🐞 Bug fix – Non-breaking change which fixes an issue
• 🚀 New feature – Non-breaking change which adds functionality
• 🔨 Refactor – Non-breaking change which refactors the code base
• 💥 Breaking change – Changes that break existing functionality
• 📚 Documentation update
• 🔒 Security update
• 🧪 Tests
• 🚂 CI

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• [ x ] ✅ Tested manually
• 🤖 Ran automated end-to-end tests

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