std.http.WebSocket: Make 'upgrade: websocket' check case-insensitive

I've seen implementations in the wild that send 'Upgrade: WebSocket',
which currently fails the handshake.

From https://datatracker.ietf.org/doc/html/rfc6455:

"If the response lacks an |Upgrade| header field or the |Upgrade| header
field contains a value that is not an ASCII case-insensitive match for
the value "websocket", the client MUST _Fail the WebSocket Connection_."

Author: linusg

lib/std/http/WebSocket.zig

@@ -30,7 +30,7 @@ pub fn init(
         if (std.ascii.eqlIgnoreCase(header.name, "sec-websocket-key")) {
             sec_websocket_key = header.value;
         } else if (std.ascii.eqlIgnoreCase(header.name, "upgrade")) {
-            if (!std.mem.eql(u8, header.value, "websocket"))
+            if (!std.ascii.eqlIgnoreCase(header.value, "websocket"))
                 return false;
             upgrade_websocket = true;
         }