Avoid warning for duplicate junit-platform.properties file

When running tests in documentation from Eclipse, the
`junit-platform.properties` file from junit-vintage-engine made it to
the test runtime classpath. Setting `containsTestFixtures` to `false`
prevents that. It causes `without_test_code` to be set to `true` in
generated `.classpath` files.

Author: marcphilipp

junit-vintage-engine/junit-vintage-engine.gradle.kts

@@ -89,3 +89,10 @@ tasks {
 		dependsOn(testWithoutJUnit4)
 	}
 }
+
+eclipse {
+	classpath {
+		// Avoid exposing test resources to dependent projects
+		containsTestFixtures = false
+	}
+}