Fix max proposal code size docstring

[brentstone]

Describe your changes

The param is in bytes, not kB

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:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.03%. Comparing base (f88c4b9) to head (d79dd66).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3846   +/-   ##
=======================================
  Coverage   73.02%   73.03%           
=======================================
  Files         340      340           
  Lines      104816   104816           
=======================================
+ Hits        76543    76553   +10     
+ Misses      28273    28263   -10     

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