Fix BTPlayer.set_behavior_tree() not populating Blackboard #791

Job	Run time
⚙️ Static checks	8s
cache-env	1s
🧪 Unit tests	3m 5s
🔌 GDExtension / 🐧 Linux (x86_64, release)	26s
🪟 Windows / Editor (x86_64, release)	18m 11s
🔌 GDExtension / 🐧 Linux (x86_64, debug)	42s
🍎 macOS / Editor (x86_64, release)	3m 19s
🐧 Linux / Editor (x86_64, release)	15m 11s
🔌 GDExtension / 🪟 Windows (x86_64, release)	3m 15s
🔌 GDExtension / 🪟 Windows (x86_64, debug)	3m 28s
🐧 Linux / Template (x86_64, release)	9m 44s
🍎 macOS / Editor (arm64, release)	3m 9s
🐧 Linux / Editor .NET (x86_64, release)	16m 4s
🔌 GDExtension / 🍎 macOS (universal, release)	1m 2s
🔌 GDExtension / 🍎 macOS (universal, debug)	1m 12s
🍎 macOS / Make macOS Bundles (tmp-macos, false, true)	39s
🔌 GDExtension / 📦 Package extension	31s
🪟 Windows / .NET assembly for ${{ matrix.opts.arch }}	0s
	1h 20m 7s

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