Revert to using stash apply instead of merge (#360)

Author: fcollonval

jupyter_releaser/lib.py

@@ -172,7 +172,7 @@ def make_changelog_pr(auth, branch, repo, title, commit_message, body, dry_run=F
         pass
     util.run(f"git checkout -b {pr_branch} origin/{branch}", echo=True)
     if dirty:
-        util.run("git merge --squash --strategy-option=theirs stash", echo=True)
+        util.run("git stash apply", echo=True)
 
     # Add a commit with the message
     try: