[Kotlin/vertx-web-kotlinx(-*)] Fix a date warning with a custom kotlinx-datetime RFC 1123 format

[ShreckYe]

This happened when the second value is 0:

   WARN for http://tfb-server:8080/updates?queries=501
     Invalid Date header, found "Wed, 11 Feb 2026 00:46 GMT", did not match "%a, %d %b %Y %H:%M:%S %Z".
     See https://github.com/TechEmpower/FrameworkBenchmarks/wiki/Project-Information-Framework-Tests-Overview#specific-test-requirements