Bump cosmos-sdk version v0.42.5 to v0.42.6

[dongsam]

Description

Bump cosmos-sdk version to v0.42.6 for gaia deps cosmos/gaia#889

closes: #XXXX

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Before we can merge this PR, please make sure that all the following items have been
checked off. If any of the checklist items are not applicable, please leave them but
write a little note why.

• 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
• Review Codecov Report in the comment section below once CI passes

[codecov]

Codecov Report

Merging #426 (499a14a) into develop (332264f) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #426   +/-   ##
========================================
  Coverage    83.36%   83.36%           
========================================
  Files           20       20           
  Lines         2302     2302           
========================================
  Hits          1919     1919           
  Misses         218      218           
  Partials       165      165           

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