SDKv2 Diff tests for secret set type

[VenelinMartinov]

This adds Diff tests for the SDKv2 bridge for secrets in set types.

Fixes #2791

[VenelinMartinov]

This change is part of the following stack:

• SDKv2 Diff tests for secret primitive types #2834
  • SDKv2 Diff tests for secret list type #2835
    • SDKv2 Diff tests for secret set type #2836 ◀
      • Refactor Set and List Diff tests to use generic utilities #2837
        • SDKv2 Diff tests for Defaults in sets and lists #2838
          • SDKv2 Diff tests for MaxItemsOne sets #2839

_{Change managed by git-spice.}

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.48%. Comparing base (278674c) to head (11d0a7f).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2836      +/-   ##
==========================================
- Coverage   67.49%   67.48%   -0.01%     
==========================================
  Files         325      325              
  Lines       41633    41633              
==========================================
- Hits        28099    28097       -2     
- Misses      11954    11957       +3     
+ Partials     1580     1579       -1     

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