Fix stale values in tied parameters during fitting (closes #20710) - #20726

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@tepickering , can you pls reopen this PR and review it ?

i personally don't have the power to do that. also, although this change is small, i think it merits a changelog entry since it is a bugfix: https://docs.astropy.org/en/latest/development/development_details.html#add-a-changelog-entry

@tepickering, i have added a log entry and regression test can you review it ?