test: Default container with disabled paddings behaves as a flow layout

[Al-Dani]

Description

While adding features to the container component, it started to behave as flexbox layout by default. It was not intended by design, and was fixed afterwards.
This test will cover the use-case with empty container without paddings, where the container is just a wrapper with some styling for borders and shadows.

Related links, issue #, if available: AWSUI-20439

How has this been tested?

• One more example added to /container/simple: 'Container with disabled paddings and box'

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (9359ffd) 91.85% compared to head (741c416) 91.85%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #809   +/-   ##
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  Coverage   91.85%   91.85%           
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  Files         585      585           
  Lines       14849    14849           
  Branches     4753     4753           
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  Hits        13639    13639           
  Misses       1128     1128           
  Partials       82       82           

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