feat: point jvm to use custom krb5.conf

Author: SML0127

fluss-common/src/test/java/org/apache/fluss/security/auth/sasl/gssapi/GssapiSaslAuthTest.java

@@ -93,6 +93,9 @@ void setup() throws Exception {
             // and force it to recognize the new settings.
             File customKrb5Conf = new File(workDir, "krb5-custom-" + UUID.randomUUID() + ".conf");
             Files.write(customKrb5Conf.toPath(), krb5Content.getBytes());
+
+            // Point the JVM to use our custom krb5.conf for Kerberos operations.
+            System.setProperty("java.security.krb5.conf", customKrb5Conf.getAbsolutePath());
         }
     }