x/ibc: fix int overflow

[alessio]

x/ibc/07-tendermint/types/test_utils.go: Calculate and use
machine-dependent maxInt instead of causing int overflow by
passing math.MaxInt64.

Closes: #6130

This mitigation should be applied while we wait for tendermint
to migrate away from machine-dependent integers.

[auto-comment]

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[codecov]

Codecov Report

Merging #6171 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #6171   +/-   ##
=======================================
  Coverage   54.79%   54.79%           
=======================================
  Files         443      443           
  Lines       26704    26704           
=======================================
  Hits        14633    14633           
  Misses      11032    11032           
  Partials     1039     1039           

[fedekunze]

utACK