Only use coroutines-test in tests. (#1764)

Co-authored-by: BMItter <46747780+BMItter@users.noreply.github.com>

Corona-Warn-App/build.gradle

@@ -306,7 +306,7 @@ dependencies {
     def coroutineVersion = "1.4.2"
     implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:$coroutineVersion"
     implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:$coroutineVersion"
-    implementation "org.jetbrains.kotlinx:kotlinx-coroutines-test:$coroutineVersion"
+    testImplementation "org.jetbrains.kotlinx:kotlinx-coroutines-test:$coroutineVersion"
     implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
 
     // ANDROID STANDARD