fix(deps): update dependency com.gradleup.shadow:shadow-gradle-plugin to v8.3.9 (#759)

Co-authored-by: elastic-renovate-prod[bot] <174716857+elastic-renovate-prod[bot]@users.noreply.github.com>

Author: elastic-renovate-prod[bot]

gradle/libs.versions.toml

@@ -1,5 +1,5 @@
 [versions]
-shadow = "8.3.8"
+shadow = "8.3.9"
 jib = "3.4.5"
 spotless = "7.2.1"
 junit = "5.13.4"