Backport of Change JUnit terraform test output to include test failure details inside <failure> elements, use the error message as the message attribute into v1.11

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Backport

This PR is auto-generated from #36316 to be assessed for backporting due to the inclusion of the label 1.11-backport.

The below text is copied from the body of the original PR.

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This PR

• 1. Updates the message attribute on a <failure> element to summarise how many assertions are failing out of a given total, and includes the first failed assertion's error message.
  • This is a remaining piece of feedback on the JUnit test report shared in the Discuss forum: https://discuss.hashicorp.com/t/request-for-feedback-on-terraform-test-junit-xml-output/62307/16?u=sarah.french
• 2. Moves the rendering of the failured message diag into the element's body
  • This matches the docs for Azure Devops's use of JUnit XML format
  • This also matches feedback in this message from the Discuss forum thread

Related:

• Update docs for -junit-xml flag

Target Release

1.11.x

CHANGELOG entry

• This change is user-facing and I added a changelog entry.
• This change is not user-facing.

This change relates to a feature that isn't released yet

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Overview of commits

• 855f2e9

• 132b8bd

• d8da87e

• b0ea078

• 5aea43e

• 080505c

• b6798ae

• add24c6

• 0bbcfdd

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