flash_encryption_example: Increase timeout

examples/security/flash_encryption/pytest_flash_encryption.py

@@ -65,4 +65,4 @@ def test_examples_security_flash_encryption(dut: Dut) -> None:
         'NVS partition "custom_nvs" is encrypted.'
     ]
     for line in lines:
-        dut.expect(line, timeout=2)
+        dut.expect(line, timeout=20)