[Build] Move JUnit dependencies into the version catalog

The `kotlin-test` dependencies are left untouched as changing them affects publications, thus these versions are independent from the used inside our build
#KTI-1349 In Progress

plugins/assign-plugin/build.gradle.kts

@@ -20,7 +20,7 @@ dependencies {
     testApi(projectTests(":compiler:tests-common-new"))
 
     testImplementation(projectTests(":compiler:tests-common"))
-    testImplementation(commonDependency("junit:junit"))
+    testImplementation(libs.junit4)
 
     testCompileOnly(project(":kotlin-reflect-api"))
     testRuntimeOnly(project(":kotlin-reflect"))