types: update account pubkey JSON to string

[fedekunze]

Description

---

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

---

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)

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (development@820bf0f). Click here to learn what that means.
The diff coverage is n/a.

@@              Coverage Diff               @@
##             development     #494   +/-   ##
==============================================
  Coverage               ?   71.72%           
==============================================
  Files                  ?       40           
  Lines                  ?     2677           
  Branches               ?        0           
==============================================
  Hits                   ?     1920           
  Misses                 ?      616           
  Partials               ?      141           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 820bf0f...7dce82d. Read the comment docs.

[fedekunze]

no clue why are the rpc tests failing