update test docker file to python3

[colin-axner]

Closes: #XXX

Description

previous issue

make test-gaia
ERROR: unsatisfiable constraints:
  python (missing):

command now works

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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

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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

Merging #534 (c0bc95a) into main (d974b27) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #534   +/-   ##
=======================================
  Coverage   11.58%   11.58%           
=======================================
  Files           8        8           
  Lines         673      673           
=======================================
  Hits           78       78           
  Misses        586      586           
  Partials        9        9