Alternative `format_source` fix #31127

Job	Run time
setup-selenium / setup_chromedriver	2s
build-client / build-client	10m 15s
Test (3.8, 0)	41m 20s
Test (3.8, 1)	48m 30s
Test (3.8, 2)	46m 3s
	2h 26m 10s

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