Add volume definition for semaphore state

Remove unused config file env var

Dockerfile

@@ -28,8 +28,6 @@ FROM python:3.11-slim
 ARG OPENTOFU_VERSION
 ARG SEMAPHORE_VERSION
 
-ENV SEMAPHORE_RUNNER_CONFIG_FILE /semaphore/config.json
-
 COPY --from=build /build/wheels /tmp/wheels
 
 RUN apt-get update --yes && \
@@ -52,10 +50,11 @@ RUN apt-get update --yes && \
     --no-cache-dir \
     --find-links /tmp/wheels \
     --disable-pip-version-check && \
-  rm -rf /tmp/wheels && \
-  mkdir --parents /semaphore
+  rm -rf /tmp/wheels
 
 ADD entrypoint.sh /entrypoint.sh
 ADD configure.py /configure.py
 
+VOLUME /semaphore
+
 ENTRYPOINT ["/entrypoint.sh"]