Values in generic types are only available in 6.2

rdar://142781302

Author: etcwilde

stdlib/public/core/Slab.swift

@@ -11,7 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 /// A fixed-size array.
-@available(SwiftStdlib 6.1, *)
+@available(SwiftStdlib 6.2, *)
 @frozen
 public struct Slab<let count: Int, Element: ~Copyable>: ~Copyable {
   @usableFromInline