More multisig tests (backport #4289)

[mergify]

Describe your changes

Adds a few more cases to the multisig unit test aimed at covering some possible misbehaviors by one of the participants in the multisig account.

Checklist before merging

• If this PR has some consensus breaking changes, I added the corresponding breaking:: labels
  • This will require 2 reviewers to approve the changes
• If this PR requires changes to the docs or specs, a corresponding PR is opened in the namada-docs repo
  • Relevant PR if applies:
• If this PR affects services such as namada-indexer or namada-masp-indexer, a corresponding PR is opened in that repo
  • Relevant PR if applies:

---

This is an automatic backport of pull request #4289 done by [Mergify](https://mergify.com).

[codecov]

Codecov Report

Attention: Patch coverage is 96.39640% with 4 lines in your changes missing coverage. Please review.

Project coverage is 74.06%. Comparing base (dc1aef1) to head (e27d3cd).
Report is 9 commits behind head on maint-libs-0.47.

Files with missing lines	Patch %	Lines
crates/tx/src/types.rs	96.39%	4 Missing ⚠️

Additional details and impacted files

@@                 Coverage Diff                 @@
##           maint-libs-0.47    #4295      +/-   ##
===================================================
+ Coverage            74.04%   74.06%   +0.01%     
===================================================
  Files                  345      345              
  Lines               110033   110155     +122     
===================================================
+ Hits                 81475    81584     +109     
- Misses               28558    28571      +13     

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