[backport 2.3.x] TST (string dtype): avoid explicit object dtype Index in fixture data (#60217) #20084

Job	Run time
Linux-Musl	17m 57s
Linux-32-bit	20m 29s
python-dev (macOS-13)	36m 52s
python-dev (macOS-14)	14m 37s
python-dev (ubuntu-22.04)	24m 3s
python-dev (windows-latest)	27m 7s
macos-13 actions-310.yaml	45m 37s
macos-13 actions-311.yaml	37m 50s
macos-13 actions-312.yaml	44m 31s
macos-13 actions-39.yaml	31m 41s
macos-14 actions-310.yaml	24m 31s
macos-14 actions-311.yaml	24m 23s
macos-14 actions-312.yaml	22m 53s
macos-14 actions-39.yaml	29m 21s
windows-latest actions-311.yaml	40m 29s
windows-latest actions-310.yaml	56m 38s
windows-latest actions-312.yaml	46m 42s
windows-latest actions-39.yaml	38m 40s
ubuntu-latest actions-310.yaml	52m 13s
Copy-on-Write 3.10 (warnings)	28m 51s
Copy-on-Write 3.10	29m 2s
ubuntu-latest actions-311.yaml	48m 30s
Future infer strings (without pyarrow)	49m 4s
Locale: zh_CN	28m 19s
Copy-on-Write 3.11	27m 42s
Copy-on-Write 3.11 (warnings)	28m 54s
Locale: it_IT	29m 37s
Downstream Compat	6m 27s
Numpy Dev	23m 53s
Pyarrow Nightly	24m 6s
ubuntu-latest actions-312.yaml	37m 53s
Future infer strings	41m 43s
Copy-on-Write 3.12	31m 46s
ubuntu-latest actions-39.yaml	48m 12s
Copy-on-Write 3.9 (warnings)	27m 56s
Minimum Versions	28m 38s
Pypy	7m 51s
Copy-on-Write 3.9	28m 38s
	20h 13m 36s

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