PF Diff tests for secrets

[VenelinMartinov]

This change adds tests for PF handling of secrets in previews.

This covers:

• secret attributes
• secrets elements in set attributes,
• secret collection attributes
• secrets properties in blocks
• secret blocks
• secrets coming from pulumi schema

[VenelinMartinov]

This change is part of the following stack:

• 2640

  • 2642 ◀

    • 2628

      • 2629

        • 2643

_{Change managed by git-spice.}

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 69.97%. Comparing base (bef446f) to head (ad7f844). Report is 2 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2642 +/- ## ======================================= Coverage 69.97% 69.97% ======================================= Files 367 367 Lines 44503 44503 ======================================= + Hits 31140 31141 +1 - Misses 11734 11735 +1 + Partials 1629 1627 -2 ```

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[pulumi-bot]

This PR has been shipped in release v3.96.0.