build(docker): fix docker build failing due to file rename

Author: OliverDudgeon

Dockerfile

@@ -55,7 +55,7 @@ ENV NODE_ENV production
 RUN addgroup --system --gid 1001 nodejs
 RUN adduser --system --uid 1001 nextjs
 
-COPY --from=builder /app/next.config.js ./
+COPY --from=builder /app/next.config.mjs ./
 COPY --from=builder /app/public ./public
 COPY --from=builder /app/package.json ./package.json
 COPY --from=builder /app/.env ./.env