fix: explain transport host rejections #2548

Job	Run time
checks / readme-snippets	11s
checks / pre-commit	31s
checks / test (3.11, lowest-direct, windows-latest)	1m 25s
checks / test (3.10, lowest-direct, windows-latest)	1m 16s
checks / test (3.10, locked, windows-latest)	1m 24s
checks / test (3.11, lowest-direct, ubuntu-latest)	47s
checks / test (3.10, lowest-direct, ubuntu-latest)	54s
checks / test (3.11, locked, ubuntu-latest)	46s
checks / test (3.10, locked, ubuntu-latest)	46s
checks / test (3.12, locked, ubuntu-latest)	52s
checks / test (3.12, lowest-direct, ubuntu-latest)	53s
checks / test (3.13, lowest-direct, ubuntu-latest)	47s
checks / test (3.12, lowest-direct, windows-latest)	1m 23s
checks / test (3.12, locked, windows-latest)	1m 29s
checks / test (3.11, locked, windows-latest)	1m 23s
checks / test (3.14, lowest-direct, windows-latest)	1m 12s
checks / test (3.13, locked, ubuntu-latest)	48s
checks / test (3.13, locked, windows-latest)	1m 13s
checks / test (3.14, locked, windows-latest)	2m 3s
checks / test (3.13, lowest-direct, windows-latest)	1m 29s
checks / test (3.14, lowest-direct, ubuntu-latest)	48s
checks / test (3.14, locked, ubuntu-latest)	1m 51s
all-green	3s
	24m 14s

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