FORMS-24185: add regression test for fragment without a panel

[AnurudraS]

PR #1603 (reverted, see FORMS-24163) assumed every fragment's label container used the generic panel class, which threw when a fragment's fragmentPath resolved directly to fields with no wrapping panel. The existing fixture (test-fragment) always wraps fields in a panel, so this shape went uncaught. Reuses the existing container-rules.html page, which already embeds a panel-less fragment.

Description

Related Issue

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes and the overall coverage did not decrease.
• All unit tests pass on CircleCi.
• I ran all tests locally and they pass.

[adobe-bot]

Accessibility Violations Found

Id	Impact
aria-required-attr	critical
empty-heading	minor
label-title-only	serious
page-has-heading-one	moderate
target-size	serious

[adobe-bot]

Accessibility Violations Found

Id	Impact
aria-required-attr	critical
empty-heading	minor
label-title-only	serious
target-size	serious

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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