Fix format

Author: Avery-Dunn

msal4j-sdk/src/test/java/com/microsoft/aad/msal4j/DateTimeTests.java

@@ -38,7 +38,7 @@ void parseIso8601Format() {
     @ParameterizedTest
     @ValueSource(strings = {
             "2025-05-15T12:34:56Z",              // Basic UTC format
-            "2025-05-15T12:34:56.1234",          // With milliseconds
+            "2025-05-15T12:34:56.1234Z",          // With milliseconds
             "2025-05-15T12:34:56.123456789Z"     // With nanoseconds
     })
     void testValidIso8601Formats(String timestamp) {