Use 'min' instead of hardcoded Julia 1.6 in CI test matrix

julia-actions/setup-julia resolves 'min' from [compat] julia in Project.toml.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ViralBShah

.github/workflows/test.yml

@@ -22,7 +22,7 @@ jobs:
         version:
           - '1'    # Current stable version
           - 'lts'  # Current LTS version
-          - '1.6'  # Previous LTS version
+          - 'min'  # Minimum supported version from Project.toml
         os:
           - macOS-15-intel
           - ubuntu-latest