[MISC] Use test app beta for isolated test

[dragomirp]

• Use beta branch for spaces tests (regression caused by [MISC] Conditionally create the legacy interface to support Juju 4 postgresql-test-app#368)
• Re-enable upgrade from edge test

Checklist

• I have added or updated any relevant documentation.
• I have cleaned any remaining cloud resources from my accounts.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.14%. Comparing base (695fb93) to head (2e908da).
Report is 1 commits behind head on 16/edge.

Additional details and impacted files

@@           Coverage Diff            @@
##           16/edge    #1032   +/-   ##
========================================
  Coverage    70.14%   70.14%           
========================================
  Files           16       16           
  Lines         3815     3815           
  Branches       549      549           
========================================
  Hits          2676     2676           
  Misses        1009     1009           
  Partials       130      130           

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[taurus-forever]

LGTM, please update PR description we will merge it ASAP.