increase types/module coverage up to 80%

[alessio]

Add interface tests.

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For contributor use:

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the module structure standards.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer

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For admin use:

• Added appropriate labels to PR (ex. WIP, R4R, docs, etc)
• Reviewers assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[alexanderbez]

ACK

[codecov]

Codecov Report

Merging #5740 into master will increase coverage by 0.28%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##           master   #5740      +/-   ##
=========================================
+ Coverage   36.52%   36.8%   +0.28%     
=========================================
  Files         336     336              
  Lines       32743   32743              
=========================================
+ Hits        11958   12051      +93     
+ Misses      19556   19464      -92     
+ Partials     1229    1228       -1

Impacted Files	Coverage Δ
crypto/keys/keyring.go	52.08% <0%> (ø)	⬆️
types/module/module.go	100% <0%> (+89.42%)	⬆️