BUG: Fix unpickling of string dtypes of legacy pandas versions #24235

Job	Run time
python-dev	0s
Linux-Musl	3m 0s
Linux-32-bit	3m 1s
macos-13 actions-310.yaml	2m 59s
macos-13 actions-311.yaml	3m 0s
macos-13 actions-312.yaml	3m 0s
macos-13 actions-313.yaml	2m 59s
windows-latest actions-311.yaml	2m 49s
macos-14 actions-310.yaml	3m 4s
macos-14 actions-312.yaml	2m 55s
windows-latest actions-313.yaml	2m 51s
macos-14 actions-311.yaml	2m 50s
windows-latest actions-310.yaml	2m 49s
windows-latest actions-312.yaml	2m 48s
macos-14 actions-313.yaml	2m 53s
Pyodide build	2m 57s
Locale: it_IT	2m 59s
Locale: zh_CN	2m 59s
Pypy	1m 35s
ubuntu-24.04-arm actions-310.yaml	2m 57s
Future infer strings (without pyarrow)	3m 1s
ubuntu-24.04-arm actions-311.yaml	3m 1s
ubuntu-24.04 actions-312.yaml	3m 1s
Downstream Compat	3m 15s
Pyarrow Nightly	3m 8s
ubuntu-24.04-arm actions-312.yaml	3m 0s
ubuntu-24.04 actions-311.yaml	3m 1s
Future infer strings	3m 1s
Minimum Versions	2m 56s
Numpy Dev	3m 7s
ubuntu-24.04 actions-313.yaml	3m 1s
ubuntu-24.04-arm actions-313.yaml	2m 49s
ubuntu-24.04 actions-310.yaml	3m 1s
Freethreading	3m 15s
	1h 37m 2s

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