Bump to JUnit 5 (with vintage engine)

This doesn't migrate the tests - this will happen in a separate commit.

Author: AlexandreCarlton

build.gradle

@@ -67,9 +67,11 @@ jar {
 dependencies {
     api 'org.slf4j:slf4j-api:' + slf4jVersion
     testImplementation 'org.slf4j:slf4j-simple:' + slf4jVersion
-    testImplementation 'junit:junit:4.12'
     testImplementation 'org.awaitility:awaitility:2.0.0'
     testImplementation 'com.github.ben-manes.caffeine:caffeine:2.9.0'
+
+    testImplementation platform('org.junit:junit-bom:5.10.2')
+    testImplementation 'org.junit.vintage:junit-vintage-engine'
 }
 
 task sourcesJar(type: Jar) {