Revert to using stash apply instead of merge

[fcollonval]

In #358, the logic to create the changelog PR was updated to use git merge instead git stash (presumably to be more robust in case of changes are pulled from the upstream branch).

In JupyterLab, this results in the bump by lerna of node packages to be committed with the Changelog changes as a commit is done automatically by lerna in the bump version step. The reason is that the merge command on the stash branch is bringing in more than the change stashed.

Failing PR example: jupyterlab/jupyterlab#12932

[codecov-commenter]

Codecov Report

Merging #360 (f584ed5) into main (03e5899) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #360   +/-   ##
=======================================
  Coverage   78.60%   78.60%           
=======================================
  Files          21       21           
  Lines        2734     2734           
  Branches      352      352           
=======================================
  Hits         2149     2149           
  Misses        467      467           
  Partials      118      118           

Impacted Files	Coverage Δ
jupyter_releaser/lib.py	80.69% <100.00%> (ø)

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[fcollonval]

Other issue related to the use of git merge:

Just tried with a simple extension and while the changelog PR is correctly generated: jupyterlab-contrib/jupyterlab-cell-flash#32

The check release workflow fails with the following: https://github.com/jupyterlab-contrib/jupyterlab-cell-flash/runs/7766995009?check_suite_focus=true

COMMAND: git checkout -b changelog-f910df6e18aa11ed9f1611ea265f32fd origin/main
Switched to a new branch 'changelog-f910df6e18aa11ed9f1611ea265f32fd'
branch 'changelog-f910df6e18aa11ed9f1611ea265f32fd' set up to track 'origin/main'.
COMMAND: git merge --squash --strategy-option=theirs stash
merge: stash - not something we can merge

So yeah probably #360 will help with this.

Originally posted by @jtpio in jupyterlab/jupyterlab#12932 (comment)

[jtpio]

This should also help fix other failures happening in the check_release workflow as mentioned in jupyterlab/jupyterlab#12932 (comment).

[fcollonval]

This patch does fix the changelog generation for JupyterLab: jupyterlab/jupyterlab#12933

[blink1073]

Hmm, the git stash was failing when making an automated changelog PR to releaser itself, but we'll have to accept that limitation considering the effect it is having on JupyterLab.

[jtpio]

Just tried with a simple extension and while the changelog PR is correctly generated: jupyterlab-contrib/jupyterlab-cell-flash#32

Re-running the failed workflow, the git stash apply now gives the following: https://github.com/jupyterlab-contrib/jupyterlab-cell-flash/runs/7781697685?check_suite_focus=true

COMMAND: git stash apply
Auto-merging CHANGELOG.md
CONFLICT (content): Merge conflict in CHANGELOG.md
On branch changelog-f286a812194111eda8add14d98809210
Your branch is up to date with 'origin/main'.

Unmerged paths:
  (use "git restore --staged <file>..." to unstage)
  (use "git add <file>..." to mark resolution)
	both modified:   CHANGELOG.md

no changes added to commit (use "git add" and/or "git commit -a")

[fcollonval]

Could it be that it comes from the fetch being done before the stash?

Ref: https://github.com/jupyter-server/jupyter_releaser/pull/358/files#diff-ca135d2d777d63b28c1452f7a690b95977a6eac5fbed4081fb948a80b2b156f5

[blink1073]

Okay, this approach is problematic, I'm just going to revert to what we had originally.