fix(sessions): use image pull secret from private build registry correctly (#1274)

* fix: don-t recreate private image pull secret

When retrieving the image pull secret to be used by a session, if
it's an existing secret, do not add it to the extra resources to
be created.

This is the case for the registry used to store the images built
out of private repositories.

Author: sgaist

components/renku_data_services/notebooks/core_sessions.py

@@ -928,7 +928,8 @@ async def start_session(
         image_check_repo=image_check_repo,
         builds_config=builds_config,
     )
-    if image_secret:
+
+    if image_secret and image_secret.secret.data is not None:
         session_extras = session_extras.concat(SessionExtraResources(secrets=[image_secret]))
 
     # Remote session configuration
@@ -1243,7 +1244,8 @@ async def patch_session(
         builds_config=builds_config,
     )
     if image_pull_secret:
-        session_extras = session_extras.concat(SessionExtraResources(secrets=[image_pull_secret]))
+        if image_pull_secret.secret.data is not None:
+            session_extras = session_extras.concat(SessionExtraResources(secrets=[image_pull_secret]))
         patch.spec.imagePullSecrets = [ImagePullSecret(name=image_pull_secret.name, adopt=image_pull_secret.adopt)]
     else:
         patch.spec.imagePullSecrets = RESET