Moved workflow samples out of .github/workflows

The `.github/workflows` directory has additional permissions attached, preventing these
files from being by the Upgrade Gradle Wrapper plugin.

.github/workflow-samples/groovy-dsl/build.gradle

@@ -0,0 +1,22 @@
+plugins {
+    id 'java'
+}
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    testImplementation('junit:junit:4.13.2')
+}
+
+tasks.named("test").configure {
+    // Echo an output value so we can detect configuration-cache usage
+    println "::set-output name=task_configured::yes"
+
+    doLast {
+        if (System.properties.verifyCachedBuild) {
+            throw new RuntimeException("Build was not cached: unexpected execution of test task")
+        }
+    }
+}