Update plugin buildconfig to v5.6.8 (#189)

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

Author: renovate[bot]

gradle/libs.versions.toml

@@ -21,6 +21,6 @@ kotlinx-metadata-klib = { module = "org.jetbrains.kotlinx:kotlinx-metadata-klib"
 mavenPublish-gradle-plugin = { module = "com.vanniktech:gradle-maven-publish-plugin", version = "0.34.0" }
 
 [plugins]
-buildconfig = { id = "com.github.gmazzo.buildconfig", version = "5.6.7" }
+buildconfig = { id = "com.github.gmazzo.buildconfig", version = "5.6.8" }
 spotless = { id = "com.diffplug.spotless", version = "6.25.0" }
 burst-kotlin = { id = "app.cash.burst.kotlin" }