Add if !os(WASI) for SwiftWasm (#31)

Author: inamiy

Sources/XCTestDynamicOverlay/XCTIsTesting.swift

@@ -1,9 +1,11 @@
 import Foundation
 
+#if !os(WASI)
 public let _XCTIsTesting: Bool = {
   ProcessInfo.processInfo.environment.keys.contains("XCTestSessionIdentifier")
     || ProcessInfo.processInfo.arguments.first
       .flatMap(URL.init(fileURLWithPath:))
       .map { $0.lastPathComponent == "xctest" || $0.pathExtension == "xctest" }
       ?? false
 }()
+#endif