Update codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/testutil/Rust.kt

Co-authored-by: John DiSanti <johndisanti@gmail.com>

Author: thomas-k-cameron

codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/testutil/Rust.kt

@@ -43,7 +43,7 @@ import java.nio.file.Path
 import kotlin.io.path.absolutePathString
 
 // cargo commands and env values
-object Commands {
+private object Commands {
     private const val cfgUnstable = "--cfg aws_sdk_unstable"
     fun func(s: String, add: String, flag: Boolean): String {
         if (flag) {