Fix f-string middle panic when parsing t-strings (#23232)
Summary
--
This PR fixes #23198 by copying Dylan's changes from #19183 to the other
`InterpolatedStringElementsKind` variant, in line with Micha's prophetic
comment
(https://github.com/astral-sh/ruff/pull/19183/changes#r2217325217).
Test Plan
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Two new tests derived from the issue
