Fix bug in api/contents requests for an allowed copy

[kiersten-stokes]

As pointed out in this comment, #937 introduced a bug in api/contents POST copy_from requests, leading to both _copy and a _new_untitled executing for an allowed copy. This PR fixes that bug by adding the else clause for the copy_from block.

Tested manually to ensure no untitled file is created on duplicate or copy/paste.

[codecov-commenter]

Codecov Report

Merging #939 (e7b010c) into main (54164ac) will not change coverage.
The diff coverage is 60.00%.

@@           Coverage Diff           @@
##             main     #939   +/-   ##
=======================================
  Coverage   72.30%   72.30%           
=======================================
  Files          65       65           
  Lines        8001     8001           
  Branches     1336     1336           
=======================================
  Hits         5785     5785           
  Misses       1810     1810           
  Partials      406      406           

Impacted Files	Coverage Δ
jupyter_server/services/contents/handlers.py	86.63% <60.00%> (ø)

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[kevin-bates]

Thank you for the quick turnaround @kiersten-stokes!

[blink1073]

@meeseeksdev please backport to 1.x

[lumberbot-app]

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

git checkout 1.x
git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

git cherry-pick -x -m1 a8bf3f6f3949e3a6ae0398386d59b5cdc432d461

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

git commit -am 'Backport PR #939: Fix bug in `api/contents` requests for an allowed copy'

4. Push to a named branch:

git push YOURFORK 1.x:auto-backport-of-pr-939-on-1.x

5. Create a PR against branch 1.x, I would have named this PR:

"Backport PR #939 on branch 1.x (Fix bug in api/contents requests for an allowed copy)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the Still Needs Manual Backport label once the PR gets merged.

If these instructions are inaccurate, feel free to suggest an improvement.