QUIC TSERVER: Fix erroneously static variable

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
(Merged from #22828)

ssl/quic/quic_tserver.c

@@ -53,7 +53,7 @@ static int alpn_select_cb(SSL *ssl, const unsigned char **out,
     static const unsigned char alpndeflt[] = {
         8, 'o', 's', 's', 'l', 't', 'e', 's', 't'
     };
-    static const unsigned char *alpn;
+    const unsigned char *alpn;
     size_t alpnlen;
 
     if (srv->args.alpn == NULL) {