Added marker condif to pytest.ini
diff --git a/pytest.ini b/pytest.ini
index f717693..9b44f19 100644
--- a/pytest.ini
+++ b/pytest.ini
@@ -9,4 +9,5 @@
     pbkdf2hmac: this test requires a backend providing PBKDF2HMACBackend
     rsa: this test requires a backend providing RSABackend
     traditional_openssl_serialization: this test requires a backend providing TraditionalOpenSSLSerializationBackend
+    pkcs8_serialization: this test requires a backend providing PKCS8SerializationBackend
     supported: parametrized test requiring only_if and skip_message