Bump io.ktor.plugin from 2.3.8 to 2.3.9 in /ktor-app

Bumps io.ktor.plugin from 2.3.8 to 2.3.9.

---
updated-dependencies:
- dependency-name: io.ktor.plugin
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

ktor-app/build.gradle.kts

@@ -5,7 +5,7 @@ val postgres_version: String by project
 
 plugins {
   kotlin("jvm") version "1.9.22"
-  id("io.ktor.plugin") version "2.3.8"
+  id("io.ktor.plugin") version "2.3.9"
   id("org.jetbrains.kotlin.plugin.serialization") version "1.9.22"
 }