SAPI should not add charset to each text subtype

Description

The built-in webserver will add ";charset=UTF-8" to the end of the Content-Type response header of the SSE response

The following code:

<?php
header('Content-Type: text/event-stream');
for ($i = 0; $i < 3; ++$i) {
    echo 'data: ' . $i . "\n\n";
}

Run server:

php -S 127.0.0.1:8080 test.php

Test:

curl http://127.0.0.1:8080/ -vvv

Resulted in this output:

# curl http://127.0.0.1:8080/ -vvv
*   Trying 127.0.0.1:8080...
* TCP_NODELAY set
* Connected to 127.0.0.1 (127.0.0.1) port 8080 (#0)
> GET / HTTP/1.1
> Host: 127.0.0.1:8080
> User-Agent: curl/7.68.0
> Accept: */*
>
* Mark bundle as not supporting multiuse
< HTTP/1.1 200 OK
< Host: 127.0.0.1:8080
< Date: Fri, 28 Apr 2023 02:51:28 GMT
< Connection: close
< X-Powered-By: PHP/8.1.18
< Content-type: text/event-stream;charset=UTF-8
<
data: 0

data: 1

data: 2

* Closing connection 0

But I expected this output instead:

# curl http://127.0.0.1:8080/ -vvv
*   Trying 127.0.0.1:8080...
* TCP_NODELAY set
* Connected to 127.0.0.1 (127.0.0.1) port 8080 (#0)
> GET / HTTP/1.1
> Host: 127.0.0.1:8080
> User-Agent: curl/7.68.0
> Accept: */*
>
* Mark bundle as not supporting multiuse
< HTTP/1.1 200 OK
< Host: 127.0.0.1:8080
< Date: Fri, 28 Apr 2023 02:51:28 GMT
< Connection: close
< X-Powered-By: PHP/8.1.18
< Content-type: text/event-stream
<
data: 0

data: 1

data: 2

* Closing connection 0

PHP Version

PHP 8.0.28, 8.1.18, 8.2.5

Operating System

No response

Start by reproducing the built-in webserver response with the PHP script and curl command shown in the issue, then trace the SAPI response-header handling for text/event-stream. Done means the response preserves Content-Type: text/event-stream without the automatically appended charset, with the existing SSE body still returned.