fix: drop stale astropy <=7.2.0 cap (floors, not pins)

[Jammy2211]

Summary

astropy was capped at >=5.0,<=7.2.0, so a fresh pip install autoarray downgrades astropy to 7.2.0 even though the stack runs and passes under 8.0.1 (PyPI latest). Drop the cap and keep the floor — astropy>=5.0 — matching the floors-not-pins convention this dependency block already documents (#433) and the uncapped astropy floors PyAutoFit / PyAutoNerves already declare.

Part of #434; a sibling PyAutoGalaxy PR carries the same floor change.

API Changes

None — internal changes only.

Test Plan

• pytest test_autoarray/ — 929 passed under astropy 8.0.1
• Clean-venv pip install --dry-run: resolves astropy 8.0.1 (control on capped main: 7.2.0)
• FITS-loaded imaging fit smoke under astropy 8.0.1

Full API Changes (for automation & release notes)

None — dependency-metadata change only (pyproject.toml astropy specifier >=5.0,<=7.2.0 → >=5.0).

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