docs: fix sentence fragment in testing guide #2634

Job	Run time
checks / readme-snippets	14s
checks / pre-commit	39s
checks / test (3.11, lowest-direct, ubuntu-latest)	55s
checks / test (3.10, locked, ubuntu-latest)	54s
checks / test (3.11, locked, ubuntu-latest)	51s
checks / test (3.10, lowest-direct, ubuntu-latest)	51s
checks / test (3.12, lowest-direct, windows-latest)	1m 33s
checks / test (3.14, lowest-direct, ubuntu-latest)	52s
checks / test (3.10, locked, windows-latest)	1m 14s
checks / test (3.14, locked, ubuntu-latest)	1m 50s
checks / test (3.11, locked, windows-latest)	1m 29s
checks / test (3.12, locked, ubuntu-latest)	52s
checks / test (3.10, lowest-direct, windows-latest)	1m 51s
checks / test (3.14, lowest-direct, windows-latest)	1m 23s
checks / test (3.13, lowest-direct, ubuntu-latest)	55s
checks / test (3.11, lowest-direct, windows-latest)	1m 23s
checks / test (3.13, locked, ubuntu-latest)	49s
checks / test (3.12, lowest-direct, ubuntu-latest)	58s
checks / test (3.14, locked, windows-latest)	2m 32s
checks / test (3.13, locked, windows-latest)	1m 18s
checks / test (3.12, locked, windows-latest)	1m 12s
checks / test (3.13, lowest-direct, windows-latest)	1m 21s
all-green	4s
	26m 0s

Provide feedback