transfer: small improvements to authz

[crodriguezvega]

Description

This PR fixes 2 out of the 3 Improvements suggested by @fedekunze here.

closes: #XXXX

Commit Message / Changelog Entry

N/A

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• 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.
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• Wrote unit and integration tests.
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[codecov-commenter]

Codecov Report

Merging #3460 (2ca365d) into main (c043dbd) will increase coverage by 0.22%.
The diff coverage is 96.77%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3460      +/-   ##
==========================================
+ Coverage   78.54%   78.76%   +0.22%     
==========================================
  Files         181      181              
  Lines       12581    12589       +8     
==========================================
+ Hits         9882     9916      +34     
+ Misses       2265     2248      -17     
+ Partials      434      425       -9     

Impacted Files	Coverage Δ
modules/core/keeper/msg_server.go	54.78% <50.00%> (-0.02%)	⬇️
modules/apps/29-fee/keeper/grpc_query.go	90.52% <100.00%> (+14.59%)	⬆️
...ules/apps/transfer/types/transfer_authorization.go	91.56% <100.00%> (+0.31%)	⬆️

[damiannolan]

Nice one! Thanks @crodriguezvega <3

[chatton]

LGTM nice improvement!