try to fix yarn install in ci

Author: rapnuss

dockerimage/Dockerfile

@@ -14,11 +14,10 @@ RUN openssl genrsa -out /tmp/private_rsa.pem 2048 \
 FROM node:22-alpine AS frontend-build
 WORKDIR /app/frontend
 RUN apk add --no-cache openssl git
-ENV YARN_CACHE_FOLDER=/root/.cache/yarn
 RUN yarn config set network-timeout 600000 \
   && yarn config set registry https://registry.npmjs.org/
 COPY frontend/package.json frontend/yarn.lock ./
-RUN --mount=type=cache,target=/root/.cache/yarn yarn install --frozen-lockfile --network-timeout 600000 --prefer-offline
+RUN yarn install --frozen-lockfile --network-timeout 600000
 COPY frontend/ .
 # Use generated public key so the static bundle verifies backend JWTs
 COPY --from=keys /tmp/public.pem ./jwt-public.pub