Improve JUnit dependencies

This commit groups the testImplementation and testRuntimeOnly
dependencies. It also depends on junit-jupiter-engine specifically at
test runtime, rather than all of junit-jupiter. This is the
configuration shown in the JUnit documentation.

Signed-off-by: Graham <gpe@openrs2.org>

build.gradle.kts

@@ -128,6 +128,9 @@ configure(subprojects.filter { it.isFree }) {
                     strictly(Versions.junit)
                 }
             }
+
+            val testRuntimeOnly by configurations
+            testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine:${Versions.junit}")
         }
     }
 
@@ -219,13 +222,6 @@ configure(subprojects.filter { it.isFree }) {
         }
     }
 
-    plugins.withType<JavaPlugin> {
-        dependencies {
-            val testRuntimeOnly by configurations
-            testRuntimeOnly("org.junit.jupiter:junit-jupiter:${Versions.junit}")
-        }
-    }
-
     plugins.withType<ApplicationPlugin> {
         dependencies {
             val runtimeOnly by configurations