Keep Docker moving tags variant-specific

[francois-drielsma]

Summary

• disable docker/metadata-action implicit semver latest generation
• retain explicit latest for the lean image and larcv for the LArCV image
• prevent slower matrix jobs from racing to overwrite the other flavor moving tag

Validation

• pre-commit check-yaml passed
• registry inspection exposed the issue: 1.2.0 was lean while latest had the 1.2.0-larcv digest

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (560010c) to head (83f52f3).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main        #5   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           11        11           
  Lines         1960      1960           
=========================================
  Hits          1960      1960           

Flag	Coverage Δ
unittests	100.00% <ø> (ø)

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