fix(STEF-2802): anchor mlflow gitignore patterns to repo root (#814)

The bare 'mlflow' pattern matched anywhere in the tree, which caused
hatchling to exclude packages/openstef-models/src/openstef_models/integrations/mlflow/
from the built wheel. Root-anchoring with '/mlflow' limits the match to
only the top-level mlflow directory (local MLflow data).

Broken since v4.0.0.a17 (commit 1bcf71d).

Signed-off-by: Egor Dmitriev <egor.dmitriev@alliander.com>

Author: egordm

.gitignore

@@ -127,5 +127,5 @@ certificates/
 benchmark_results*/
 
 # Mlflow
-mlflow
-mlflow_artifacts_local
+/mlflow
+/mlflow_artifacts_local