BUG: fix construction of Series / Index from dict keys when "str" dtype is specified explicitly #20691

Job	Run time
Pyodide build	17m 46s
Linux-32-bit	17m 36s
Linux-Musl	17m 34s
macos-13 actions-310.yaml	17m 53s
macos-13 actions-311.yaml	17m 53s
macos-13 actions-312.yaml	17m 52s
macos-14 actions-310.yaml	17m 55s
macos-14 actions-311.yaml	17m 53s
macos-14 actions-312.yaml	17m 52s
windows-latest actions-311.yaml	17m 45s
windows-latest actions-312.yaml	17m 45s
windows-latest actions-310.yaml	17m 45s
python-freethreading	17m 47s
ubuntu-latest actions-310.yaml	22m 30s
Minimum Versions	17m 45s
ubuntu-latest actions-311.yaml	22m 31s
Future infer strings (without pyarrow)	22m 33s
Locale: zh_CN	17m 48s
Locale: it_IT	17m 47s
Downstream Compat	5m 46s
Numpy Dev	17m 47s
Pyarrow Nightly	17m 49s
ubuntu-latest actions-312.yaml	22m 32s
Future infer strings	22m 32s
Pypy	1m 9s
python-dev (macOS-13)	17m 48s
python-dev (macOS-14)	15m 16s
python-dev (ubuntu-22.04)	17m 45s
python-dev (windows-latest)	17m 40s
	8h 28m 14s

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