Restrict httpx version to <1.0.0 #1643

Job	Run time
checks / pre-commit	31s
checks / readme-snippets	12s
checks / test (3.10, locked, ubuntu-latest)	50s
checks / test (3.10, locked, windows-latest)	2m 8s
checks / test (3.12, lowest-direct, windows-latest)	3m 25s
checks / test (3.12, locked, windows-latest)	3m 12s
checks / test (3.12, locked, ubuntu-latest)	53s
checks / test (3.11, lowest-direct, ubuntu-latest)	56s
checks / test (3.10, lowest-direct, windows-latest)	2m 25s
checks / test (3.10, lowest-direct, ubuntu-latest)	53s
checks / test (3.13, lowest-direct, windows-latest)	3m 28s
checks / test (3.11, locked, ubuntu-latest)	48s
checks / test (3.12, lowest-direct, ubuntu-latest)	56s
checks / test (3.11, locked, windows-latest)	2m 25s
checks / test (3.13, locked, ubuntu-latest)	47s
checks / test (3.11, lowest-direct, windows-latest)	2m 53s
checks / test (3.14, lowest-direct, windows-latest)	2m 8s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 13s
checks / test (3.13, locked, windows-latest)	2m 20s
checks / test (3.14, locked, windows-latest)	3m 1s
checks / test (3.13, lowest-direct, ubuntu-latest)	51s
checks / test (3.14, locked, ubuntu-latest)	2m 32s
all-green	4s
	38m 51s

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