add corepack enable step outside of the BUILD_ALL condition

so yarn is directly available even if built with BUILD_ALL=0

Dockerfile

@@ -283,10 +283,12 @@ ARG BUILD_ALL=1
 # install php and js dependencies and build assets
 # avoid installing cypress
 ENV CYPRESS_INSTALL_BINARY=0
+# enable new yarn
+RUN corepack enable
 # some ini settings are set on the command line to override the restrictive production ones already set
 # IMPORTANT: the yarn/build step must be done before the composer/install step because a source file (advancedQuery) will be generated by yarn
 # so in order for composer to take it into account, it must exist before we call the install command of composer.
-RUN if [ "$BUILD_ALL" = "1" ]; then corepack enable && yarn install \
+RUN if [ "$BUILD_ALL" = "1" ]; then yarn install \
     && yarn run buildall:prod \
     && /usr/bin/php81 -d memory_limit=256M -d open_basedir='' /usr/bin/composer install --prefer-dist --no-cache --no-progress --no-dev -a \
     && yarn cache clean && rm -r /root/.cache /root/.yarn; fi