fix: logging message when still using flask_env

Signed-off-by: GustaafL <guus@seita.nl>

flexmeasures/utils/config_utils.py

@@ -74,18 +74,18 @@ def read_config(app: Flask, custom_path_to_config: str | None):
 
     flexmeasures_env = DefaultConfig.FLEXMEASURES_ENV_DEFAULT
     if app.testing:
+        print("A")
         flexmeasures_env = "testing"
     elif os.getenv("FLEXMEASURES_ENV", None):
+        print("B")
         flexmeasures_env = os.getenv("FLEXMEASURES_ENV", None)
     elif os.getenv("FLASK_ENV", None):
+        print("are we getting to this point")
         flexmeasures_env = os.getenv("FLASK_ENV", None)
-        import warnings
 
-        warnings.warn(
+        app.logger.warning(
             "'FLASK_ENV' is deprecated and replaced by FLEXMEASURES_ENV"
             " Change FLASK_ENV to FLEXMEASURES_ENV in the environment variables",
-            DeprecationWarning,
-            stacklevel=2,
         )
 
     check_app_env(flexmeasures_env)