Bump playVer from 2.8.19 to 2.8.20 (#8973)

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

smoke-tests/images/play/build.gradle.kts

@@ -9,7 +9,7 @@ plugins {
   id("org.gradle.playframework") version "0.14"
 }
 
-val playVer = "2.8.19"
+val playVer = "2.8.20"
 val scalaVer = "2.12"
 
 play {