Update user agent in secrets' example

Author: codebien

release notes/v1.0.0-rc1.md

@@ -152,7 +152,7 @@ INFO[0031] {
   "headers": {
     "Custom-Authentication": "Bearer ***SECRET_REDACTED***",
     "Host": "httpbin.org",
-    "User-Agent": "k6/0.57.0 (https://k6.io/)",
+    "User-Agent": "k6/1.0.0-rc1 (https://k6.io/)",
     "X-Amzn-Trace-Id": "Root=1-67dd6691-18eeaf5d1782bf292da5037c"
   },
   "origin": "1.1.1.1",