Override Content-Length rather than appending

Author: lauzadis

runtime/protocol/http-client-engines/http-client-engine-crt/jvm/src/aws/smithy/kotlin/runtime/http/engine/crt/RequestUtil.kt

@@ -68,7 +68,7 @@ internal fun HttpRequest.toCrtRequest(callContext: CoroutineContext): aws.sdk.ko
     }
 
     val contentLength = body.contentLength?.takeIf { it >= 0 }?.toString() ?: headers[CONTENT_LENGTH_HEADER]
-    contentLength?.let { crtHeaders.append(CONTENT_LENGTH_HEADER, it) }
+    contentLength?.let { crtHeaders[CONTENT_LENGTH_HEADER] = it }
 
     return aws.sdk.kotlin.crt.http.HttpRequest(method.name, url.requestRelativePath, crtHeaders.build(), bodyStream)
 }