tests: avoid racy HTTP test ports #2427

Job	Run time
checks / readme-snippets	10s
checks / test (3.10, lowest-direct, windows-latest)	1m 23s
checks / test (3.10, locked, windows-latest)	1m 30s
checks / test (3.12, lowest-direct, ubuntu-latest)	58s
checks / test (3.13, lowest-direct, ubuntu-latest)	56s
checks / test (3.12, lowest-direct, windows-latest)	2m 25s
checks / test (3.11, locked, windows-latest)	1m 32s
checks / test (3.12, locked, windows-latest)	1m 26s
checks / test (3.13, locked, windows-latest)	1m 39s
checks / test (3.11, lowest-direct, ubuntu-latest)	58s
checks / test (3.11, lowest-direct, windows-latest)	1m 41s
checks / test (3.11, locked, ubuntu-latest)	54s
checks / test (3.10, locked, ubuntu-latest)	57s
checks / test (3.10, lowest-direct, ubuntu-latest)	56s
checks / test (3.14, locked, windows-latest)	3m 19s
checks / test (3.14, lowest-direct, ubuntu-latest)	50s
checks / test (3.13, locked, ubuntu-latest)	53s
checks / test (3.14, locked, ubuntu-latest)	1m 54s
checks / test (3.13, lowest-direct, windows-latest)	2m 2s
checks / pre-commit	37s
checks / test (3.14, lowest-direct, windows-latest)	1m 34s
checks / test (3.12, locked, ubuntu-latest)	59s
all-green	3s
	29m 36s

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