Fix WMN_CONFIG_PATH env var missing at runtime

Dockerfile

@@ -21,6 +21,7 @@ RUN groupadd -g "${WMN_GID}" wmn && \
 
 USER wmn
 ARG WMN_CONFIG_PATH=/etc/wmn/config.yml
+ENV WMN_CONFIG_PATH=$WMN_CONFIG_PATH
 WORKDIR /opt/webhook-matrix-notifier
 
 ENV PIPENV_VENV_IN_PROJECT=1

wmn/common.py

@@ -56,7 +56,7 @@ def config_path() -> pathlib.Path:
     path = pathlib.Path(path)
     path = path.absolute().resolve()
     if not path.exists():
-        raise RuntimeError("Cannot find config: " + path)
+        raise RuntimeError(f"Cannot find config: {path}")
     return path