More flexible pinning of `packaging` dependency with `>=`

[spwoodcock]

Follow on from https://github.com/dimastbk/python-calamine/pull/93 Related to https://github.com/dimastbk/python-calamine/pull/95

• Devs installing this package should have the flexibility to pin as they need.
• We can't predict if a future version of packaging will have breaking changes, so shouldn't be restrictive with approximate pinning.
• I also downgraded the minimum version of packaging back to v23.1, which was working fine prior to the upgrade in https://github.com/dimastbk/python-calamine/pull/95.
• That version was released around a year and a half ago, which should give plenty of flexibility for a minimum.