Fix: Keep `BTInstance` alive until update is finished (fixes #254) #761

Job	Run time
🧪 Unit tests	3m 0s
⚙️ Static checks	8s
cache-env	1s
🍎 macOS / Editor (x86_64, release)	3m 40s
🐧 Linux / Editor (x86_64, release)	14m 25s
🪟 Windows / Editor (x86_64, release)	17m 41s
🍎 macOS / Editor (arm64, release)	3m 15s
🔌 GDExtension / 🐧 Linux (x86_64, release)	23s
🐧 Linux / Template (x86_64, release)	10m 0s
🔌 GDExtension / 🐧 Linux (x86_64, debug)	37s
🐧 Linux / Editor .NET (x86_64, release)	16m 10s
🔌 GDExtension / 🪟 Windows (x86_64, release)	2m 39s
🔌 GDExtension / 🪟 Windows (x86_64, debug)	2m 32s
🔌 GDExtension / 🍎 macOS (universal, release)	1m 1s
🔌 GDExtension / 🍎 macOS (universal, debug)	55s
🔌 GDExtension / 📦 Package extension	29s
🍎 macOS / Make macOS Bundles (tmp-macos, false, true)	37s
🪟 Windows / .NET assembly for ${{ matrix.opts.arch }}	0s
	1h 17m 33s

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