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 #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 :white_check_mark:

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

Additional details and impacted files

```diff @@ 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 ```

[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
``