Change the type as discussed in follow-up to maplibre#47

Author: ianthetechie

Sources/MapLibreSwiftDSL/Style Layers/Symbol.swift

@@ -10,7 +10,7 @@ import MapLibreSwiftMacros
 @MLNStyleProperty<UIColor>("textColor", supportsInterpolation: true)
 @MLNStyleProperty<Double>("textFontSize", supportsInterpolation: true)
 @MLNStyleProperty<String>("text", supportsInterpolation: false)
-@MLNStyleProperty<[String]?>("textFontNames", supportsInterpolation: false)
+@MLNStyleProperty<[String]>("textFontNames", supportsInterpolation: false)
 // An enum would probably be better?
 @MLNStyleProperty<String>("textAnchor", supportsInterpolation: false)
 @MLNStyleProperty<CGVector>("textOffset", supportsInterpolation: true)