test/e2e/ibc: try to killall gaiad before running it (backport #3909)

[mergify]

Describe your changes

follow-up to #3907

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:

---

This is an automatic backport of pull request #3909 done by [Mergify](https://mergify.com).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.22%. Comparing base (7a2e3c8) to head (97b480f).
Report is 8 commits behind head on 0.44.0.

Additional details and impacted files

@@           Coverage Diff           @@
##           0.44.0    #3915   +/-   ##
=======================================
  Coverage   73.22%   73.22%           
=======================================
  Files         341      341           
  Lines      105281   105281           
=======================================
  Hits        77088    77088           
  Misses      28193    28193           

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