Blackboard: Complain when variable is missing #207

Job	Run time
🧪 Unit tests	26m 26s
cache-env	1s
🪟 Windows / Editor (x86_64, release)	46m 48s
🐧 Linux / Editor (x86_64, release)	15m 32s
🔌 GDExtension / 🐧 Linux (x86_64, release)	49s
🐧 Linux / Template (x86_64, release)	23m 13s
🔌 GDExtension / 🐧 Linux (x86_64, debug)	49s
🔌 GDExtension / 🪟 Windows (x86_64, release)	2m 13s
🍎 macOS / Editor (x86_64, release)	44m 49s
🪟 Windows / Editor .NET (x86_64, release)	12m 55s
🔌 GDExtension / 🪟 Windows (x86_64, debug)	1m 45s
🍎 macOS / Editor (arm64, release)	49m 27s
🔌 GDExtension / 🍎 macOS (universal, release)	1m 11s
🔌 GDExtension / 🍎 macOS (universal, debug)	1m 27s
🍎 macOS / Make macOS Bundles	1m 33s
	3h 48m 58s

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