Avoid stashing and checking out if volume is set

This is to avoid unpredictable behaviours

README.md

@@ -186,7 +186,7 @@ e.g., for the frontend:
 +     GITHUB_REPO: https://github.com/SciCatProject/frontend.git#v4.4.1
 ```
 
-If you did not remove the volume, specified a new branch, and had any uncommited changes, they will be stashed to checkout to the selected branch. You can later reapply them by `git stash apply`.
+The repo is checkout at that particular commit only if the docker volume does not yet exist.
 
 </details>
 

entrypoints/setup_git.sh

@@ -17,9 +17,8 @@ then
     DEFAULT_BRANCH=$(git remote show origin | sed -n '/HEAD branch/s/.*: //p')
     git reset --hard origin/"${DEFAULT_BRANCH}"
     git clean -fd
-fi
-if [ -n "${TAG}" ] && [ "${TAG}" != "$(git describe --tags)" ]
-then
-    git stash
-    git checkout "${TAG}"
+    if [ -n "${TAG}" ]
+    then
+        git checkout "${TAG}"
+    fi
 fi