Remove random password in Dockerfiles (#15362)

* Remove random password of git user in dockerfile

* Disable git user account in rootless dockerfile

Dockerfile

@@ -53,7 +53,7 @@ RUN addgroup \
     -u 1000 \
     -G git \
     git && \
-  echo "git:$(dd if=/dev/urandom bs=24 count=1 status=none | base64)" | chpasswd
+  echo "git:*" | chpasswd -e
 
 ENV USER git
 ENV GITEA_CUSTOM /data/gitea