Support string body in the generic request method #1099

Job	Run time
run-test-suite (ubuntu-latest, 3.13, latest)	10m 40s
run-test-suite (ubuntu-latest, 3.9, latest)	10m 8s
run-test-suite (ubuntu-latest, 3.9, 9.4)	11m 8s
run-test-suite (ubuntu-22.04, 3.7, 9.1)	9m 3s
	40m 59s

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