doc:change duration to duration_ns on test documentation

Author: 0xArdi-N

doc/api/test.md

@@ -2031,7 +2031,7 @@ Emitted when a test fails.
 
 * `data` {Object}
   * `details` {Object} Additional execution metadata.
-    * `duration` {number} The duration of the test in milliseconds.
+    * `duration_ms` {number} The duration of the test in milliseconds.
   * `file` {string|undefined} The path of the test file,
     `undefined` if test was run through the REPL.
   * `name` {string} The test name.