add tests: encrypt under wrong public key

[PeterChen13579]

High Level Overview of Change

Context of Change

Add tests and small checks under confidential MPT

API Impact

• Public API: New feature (new methods and/or new fields)
• Public API: Breaking change (in general, breaking changes should only impact the next api_version)
• libxrpl change (any change that may affect libxrpl or dependents of libxrpl)
• Peer protocol change (must be backward compatible or bump the peer protocol version)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.0%. Comparing base (2c94e21) to head (2542a77).
⚠️ Report is 12 commits behind head on ripple/confidential-transfer.

Additional details and impacted files

@@                      Coverage Diff                       @@
##           ripple/confidential-transfer   #6650     +/-   ##
==============================================================
- Coverage                          80.2%   80.0%   -0.2%     
==============================================================
  Files                               874     874             
  Lines                             69184   68779    -405     
  Branches                           7562    7568      +6     
==============================================================
- Hits                              55464   55034    -430     
- Misses                            13720   13745     +25     

Files with missing lines	Coverage Δ
...l/tx/transactors/token/ConfidentialMPTClawback.cpp	97.3% <100.0%> (+<0.1%)	⬆️

... and 11 files with indirect coverage changes

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