Backport of External changes report can fail with schema migrations and -target into v1.4

[teamterraform]

Backport

This PR is auto-generated from #32900 to be assessed for backporting due to the inclusion of the label 1.4-backport.

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

---

When creating a plan under the following conditions:

• A provider has been upgraded with changes to the schema
• There are external changes to resources outside of terraform
• The -target flag is being used
• Resources which are not targeted require a schema migration

The un-targeted resources will not have been migrated to a new schema and cannot be decoded from the prior state for the external changes report.

Since there is no way to decode these resources which have been excluded via -target, we can only skip over them when inspecting driftedResources. Return warnings for now to indicate that these resources could not be decoded and users will need to eventually apply these changes.

Fixes #31052

[github-actions]

Reminder for the merging maintainer: if this is a user-visible change, please update the changelog on the appropriate release branch.

[github-actions]

I'm going to lock this pull request because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active contributions.
If you have found a problem that seems related to this change, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.