tests: internal: add unsupported proxy scheme rejection cases

Add two proxy_url_checks entries that expect failure (-1) for
ftp:// and socks5:// proxy URLs, covering the rejection path
added when https:// proxy support was introduced.

Signed-off-by: Antônio Franco <13881523+antoniomrfranco@users.noreply.github.com>

Author: antoniomrfranco

tests/internal/utils.c

@@ -667,6 +667,9 @@ struct proxy_url_check proxy_url_checks[] = {
     /* HTTPS proxy with credentials */
     {0, "https://user:pass@proxy.com:443",
      "https", "proxy.com", "443", "user", "pass"},
+    /* Unsupported schemes must be rejected */
+    {-1, "ftp://proxy.com:21",  NULL, NULL, NULL, NULL, NULL},
+    {-1, "socks5://proxy.com", NULL, NULL, NULL, NULL, NULL},
 
 };