test: Optional ephemeral values do not have to be set at plan

[dsa0x]

ApplyEval expects that the only input variables are ephemeral variables that were non-null at plan time. But the test framework was sending all ephemeral variables, including the ones with a null value. However, such value means that they were also unset during plan, and the null value is a result of the default application to the variable.
Now we

1. Trigger an error only if the unexpected ephemeral value is non-null.
2. Ensure that the test framework filters out ephemeral values that the plan deem not required.

Target Release

1.17.x

Rollback Plan

• If a change needs to be reverted, we will roll out an update to the code within 7 days.

Changes to Security Controls

Are there any changes to security controls (access controls, encryption, logging) in this pull request? If so, explain.

CHANGELOG entry

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