400 when content header contains charset

[madevoge]

Some clients add a charset to the content header:
application/json;charset=UTF-8

This breaks the full equals check here:

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

Line 75 in 9f00f22

if (ct != ContentType.Application.Json) {

The following makes the equals check a bit more flexible, allowing charsets
ct.content != ContentType.Application.Json.content