chore: add androidx build test to gitignore

[erisu]

Motivation and Context

Added missing gitignore

Description

Added /test/androidx/build to .gitignore

Testing

n/a

Checklist

• I've run the tests to see all new and existing tests pass
• I added automated test coverage as appropriate for this change
• Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• I've updated the documentation if necessary

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.00%. Comparing base (bb4f86e) to head (67abd42).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1786   +/-   ##
=======================================
  Coverage   72.00%   72.00%           
=======================================
  Files          23       23           
  Lines        1850     1850           
=======================================
  Hits         1332     1332           
  Misses        518      518           

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