Update dependency io.javalin:javalin to v6.4.0 (#1205)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

gradle/libs.versions.toml

@@ -3,7 +3,7 @@ kotlin = "2.1.0"
 coroutines = "1.9.0"
 serialization = "1.7.3"
 okhttp = "5.0.0-alpha.14" # Major version is locked by Tachiyomi extensions
-javalin = "6.3.0"
+javalin = "6.4.0"
 jackson = "2.18.2" # jackson version locked by javalin, ref: `io.javalin.core.util.OptionalDependency`
 exposed = "0.57.0"
 dex2jar = "v64" # Stuck until https://github.com/ThexXTURBOXx/dex2jar/issues/27 is fixed