fix: Pass selected revision to the session container

Instead of the default branch for a git model.

backend/capellacollab/sessions/routes.py

@@ -257,15 +257,15 @@ def models_as_json(
             )
         ):
             continue
-        yield git_model_as_json(git_model, entry.deep_clone)
+        yield git_model_as_json(git_model, entry.revision, entry.deep_clone)
 
 
 def git_model_as_json(
-    git_model: git_models.DatabaseGitModel, deep_clone: bool
+    git_model: git_models.DatabaseGitModel, revision: str, deep_clone: bool
 ) -> dict[str, str | int]:
     d = {
         "url": git_model.path,
-        "revision": git_model.revision,
+        "revision": revision or git_model.revision,
         "depth": 0 if deep_clone else 1,
         "entrypoint": git_model.entrypoint,
         "nature": git_model.model.nature.name,

backend/tests/sessions/test_sessions_routes.py

@@ -344,6 +344,40 @@ def test_create_persistent_session_as_user(
     assert "/capella/remote:5.0.0" in kubernetes.sessions[0]["docker_image"]
 
 
+def test_create_read_only_session_as_user(
+    client: testclient.TestClient,
+    db,
+    user,
+    kubernetes,
+):
+    response = client.post(
+        "/api/v1/projects/default/sessions/readonly",
+        json={
+            "models": [
+                {
+                    "model_slug": "meldody-model-test-6-0-0",
+                    "git_model_id": 3,
+                    "revision": "test-branch",
+                    "deep_clone": False,
+                }
+            ]
+        },
+    )
+    out = response.json()
+    session = get_session_by_id(db, out["id"])
+
+    assert response.status_code == 200
+    assert session
+    assert session.owner_name == user.name
+    assert kubernetes.sessions
+
+    assert "/capella/readonly:6.0.0" in kubernetes.sessions[0]["docker_image"]
+    assert (
+        '"revision": "test-branch"'
+        in kubernetes.sessions[0]["environment"]["GIT_REPOS_JSON"]
+    )
+
+
 def test_create_persistent_jupyter_session(client, db, user, kubernetes):
     jupyter = create_tool(
         db,