Properly check content type. Should fix #450 (#451)

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Author: nerzhulart

kotlin-sdk-server/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/server/SSEServerTransport.kt

@@ -80,7 +80,7 @@ public class SseServerTransport(private val endpoint: String, private val sessio
 
         val body = try {
             val ct = call.request.contentType()
-            if (ct != ContentType.Application.Json) {
+            if (!ct.match(ContentType.Application.Json)) {
                 error("Unsupported content-type: $ct")
             }