BUG: Fix unpickling of string dtypes of legacy pandas versions #24234

Job	Run time
Pyodide build	21m 25s
Linux-32-bit	18m 24s
Linux-Musl	15m 20s
python-dev	0s
macos-13 actions-311.yaml	21m 21s
windows-latest actions-310.yaml	21m 18s
macos-14 actions-312.yaml	21m 19s
windows-latest actions-312.yaml	21m 15s
macos-13 actions-313.yaml	21m 22s
macos-14 actions-313.yaml	21m 25s
windows-latest actions-311.yaml	21m 14s
macos-13 actions-312.yaml	21m 22s
macos-14 actions-311.yaml	21m 31s
macos-14 actions-310.yaml	19m 49s
macos-13 actions-310.yaml	21m 18s
Locale: it_IT	21m 24s
windows-latest actions-313.yaml	21m 19s
Pyarrow Nightly	19m 4s
Future infer strings (without pyarrow)	21m 23s
ubuntu-24.04 actions-310.yaml	21m 23s
ubuntu-24.04 actions-313.yaml	21m 22s
Future infer strings	21m 22s
Pypy	1m 25s
ubuntu-24.04-arm actions-311.yaml	21m 20s
ubuntu-24.04 actions-312.yaml	21m 23s
Downstream Compat	5m 29s
ubuntu-24.04-arm actions-310.yaml	21m 19s
ubuntu-24.04-arm actions-312.yaml	21m 20s
Numpy Dev	16m 26s
Locale: zh_CN	21m 23s
Minimum Versions	21m 24s
ubuntu-24.04-arm actions-313.yaml	21m 20s
Freethreading	20m 47s
ubuntu-24.04 actions-311.yaml	21m 22s
	10h 50m 38s

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