Support string body in the generic request method #1107

Job	Run time
run-test-suite (ubuntu-latest, 3.13, latest)	10m 52s
run-test-suite (ubuntu-22.04, 3.7, 9.1)	9m 27s
run-test-suite (ubuntu-latest, 3.9, latest)	10m 24s
run-test-suite (ubuntu-latest, 3.9, 9.4)	24m 0s
	54m 43s

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