Fix the compiler version check for Span availability (#204)

Author: cmcgee1024

.swift-version

@@ -1 +1 @@
-6.1.0
+6.2.0

Package.swift

@@ -20,7 +20,8 @@ dep.append(
 
 // Enable SubprocessFoundation by default
 var defaultTraits: Set<String> = ["SubprocessFoundation"]
-#if compiler(>=6.2)
+
+#if compiler(>=6.3) || (compiler(>=6.2) && (os(Linux) || os(Windows) || os(FreeBSD)))
 // Enable SubprocessSpan when Span is available
 defaultTraits.insert("SubprocessSpan")
 #endif