ci: fix pnpm workspace detection by cleaning build environment

Dockerfile

@@ -2,6 +2,9 @@
 FROM registry.infra.mintel.me/mintel/nextjs:latest AS builder
 WORKDIR /app
 
+# Clean the workspace in case the base image is dirty
+RUN rm -rf ./*
+
 # Arguments for build-time configuration
 ARG NEXT_PUBLIC_BASE_URL
 ARG NEXT_PUBLIC_TARGET