BUG: Fix unpickling of string dtypes of legacy pandas versions #24236

Job	Run time
Linux-32-bit	19m 18s
Linux-Musl	15m 35s
python-dev	-1s
Pyodide build	23m 17s
macos-13 actions-312.yaml	31m 14s
macos-14 actions-311.yaml	22m 57s
macos-14 actions-313.yaml	23m 17s
macos-14 actions-312.yaml	21m 52s
windows-latest actions-311.yaml	35m 31s
macos-13 actions-311.yaml	34m 27s
windows-latest actions-310.yaml	34m 3s
windows-latest actions-313.yaml	40m 59s
macos-14 actions-310.yaml	26m 39s
macos-13 actions-313.yaml	28m 57s
ubuntu-24.04-arm actions-312.yaml	36m 1s
macos-13 actions-310.yaml	32m 6s
windows-latest actions-312.yaml	34m 52s
ubuntu-24.04 actions-313.yaml	47m 58s
Minimum Versions	22m 10s
Locale: zh_CN	24m 2s
Pypy	1m 27s
Locale: it_IT	23m 20s
ubuntu-24.04-arm actions-313.yaml	35m 21s
ubuntu-24.04-arm actions-310.yaml	36m 21s
Numpy Dev	17m 4s
ubuntu-24.04 actions-311.yaml	43m 30s
ubuntu-24.04-arm actions-311.yaml	35m 35s
Downstream Compat	5m 11s
Pyarrow Nightly	21m 0s
Freethreading	20m 47s
Future infer strings	44m 48s
ubuntu-24.04 actions-310.yaml	45m 42s
Future infer strings (without pyarrow)	39m 4s
ubuntu-24.04 actions-312.yaml	43m 4s
	16h 7m 28s

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