dockerfile: Add poetry lock before export for wss-proxy

The current docker build failed with Error `1.082 pyproject.toml changed significantly since poetry.lock was last generated. Run `poetry lock` to fix the lock file.`. Adding `poetry lock` command before `poetry export` will regenerate the lock file.

Changelog-None.

Author: ShahanaFarooqui

Dockerfile

@@ -243,7 +243,7 @@ RUN ./configure --prefix=/tmp/lightning_install --enable-static && poetry run ma
 
 # Export the requirements for the plugins so we can install them in builder-python stage
 WORKDIR /opt/lightningd/plugins/wss-proxy
-RUN poetry export -o requirements.txt --without-hashes
+RUN poetry lock && poetry export -o requirements.txt --without-hashes
 WORKDIR /opt/lightningd
 RUN echo 'RUSTUP_INSTALL_OPTS="${RUSTUP_INSTALL_OPTS}"' > /tmp/rustup_install_opts.txt