Add test case to document env header contains whitespace error as expected behavior.

[MicahKimel]

- What I did

• Test case to show this is expected behavior for the cli
• Documenting using a bad header in .env such as [config 1] will throw an error is expected behavior.
• closes docker run throws error if an env var contains whitespace #5057

- How to verify it

• Running test cases docker buildx bake test looked good to me

- Description for the changelog

Test case documenting using a bad header in .env will throw a error is expected behavior.

Accidentally closed [#5081], so re-opened here. Please let me know any feedback @Benehiko!

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 61.73%. Comparing base (64206ae) to head (dd80599).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5156      +/-   ##
==========================================
- Coverage   61.76%   61.73%   -0.04%     
==========================================
  Files         297      294       -3     
  Lines       20768    20763       -5     
==========================================
- Hits        12828    12817      -11     
- Misses       7024     7027       +3     
- Partials      916      919       +3     

[Benehiko]

LGTM

Could you squash all of the commits you made on this branch into a singular commit?

⋊> ~/G/docker-cli on b9ba41a8b  git log --oneline                                                                                           
b9ba41a8b (HEAD, MichaKimel/master) remove assert
1d5b2325c fix container_run.md spacing
b2b2bacf7 Add test parse env formatted badly with spaces
d69d501f6 Merge pull request #5155 from vvoland/docker-27.0-rc
...

You would want to rebase until d69d501 and squash b9ba41a, 1d5b232.

git rebase -i d69d501f6

pick b2b2bacf7 Add test parse env formatted badly with spaces
-pick 1d5b2325c fix container_run.md spacing
+squash 1d5b2325c fix container_run.md spacing
-pick b9ba41a8b remove assert
+squash b9ba41a8b remove assert

Save then edit the commit message, remove the redundant parts and make sure you have the Signed-off-by: MicahKimel <micah.kimel@my.wheaton.edu>.

Then force push, git push -f

[MicahKimel]

Thank you very much @Benehiko, now I understand how to rebase!! I went ahead and merged with upstream.

[Benehiko]

Hey @MicahKimel, thank you for taking the time to work on this. I see you have a merge commit from master into your fork's master. This should unfortunately be corrected since the project prefers rebasing your commits on top of master - this ensures a linear history on master after the PR is merged.

https://github.com/docker/cli/blob/master/CONTRIBUTING.md#conventions
https://git-scm.com/docs/git-rebase

You will most likely need to revert the last git merge upstream/master that you did and then instead run git rebase upstream/master.

Something like this (please also check this on your own):

// reset the last commit (the git merge upstream/master) (destructive!)
git reset --hard HEAD~1
// ensure you have everything from upstream
git fetch --all
// do a rebase on top of upstream/master
git rebase upstream/master
// force push to your fork's master (destructive!)
git push -f
``