Update scalatest to 3.2.18

Author: scala-steward

build.sbt

@@ -9,7 +9,7 @@ lazy val root = (project in file("."))
       "org.apache.flink"        % "flink-streaming-java"    % "1.15.0",
       "org.apache.flink"        % "flink-java"              % "1.15.0",
       "io.findify"             %% "flink-adt"               % "0.6.1",
-      "org.scalatest"          %% "scalatest"               % "3.2.12" % Test,
+      "org.scalatest"          %% "scalatest"               % "3.2.18" % Test,
       "org.apache.flink"        % "flink-test-utils"        % "1.15.0" % Test,
       "org.apache.flink"        % "flink-test-utils-junit"  % "1.15.0" % Test,
       "com.github.sbt"          % "junit-interface"         % "0.13.3" % Test,