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

❌ Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.1%. Comparing base (2c94e21) to head (8cc1afe).
⚠️ Report is 10 commits behind head on ripple/confidential-transfer.

Files with missing lines	Patch %	Lines
...l/tx/transactors/token/ConfidentialMPTClawback.cpp	50.0%	2 Missing ⚠️

Additional details and impacted files

@@                      Coverage Diff                       @@
##           ripple/confidential-transfer   #6650     +/-   ##
==============================================================
- Coverage                          80.2%   80.1%   -0.1%     
==============================================================
  Files                               874     874             
  Lines                             69184   68894    -290     
  Branches                           7562    7548     -14     
==============================================================
- Hits                              55464   55175    -289     
+ Misses                            13720   13719      -1     

Files with missing lines	Coverage Δ
...l/tx/transactors/token/ConfidentialMPTClawback.cpp	94.9% <50.0%> (-2.4%)	⬇️

... and 6 files with indirect coverage changes

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[shawnxie999]

both returns should have // LCOV_EXCL_LINE to exclude them from test coverage since they are defensive checks that are unreachable