[PR #8920/5cf5db56 backport][3.11] Re-enable keep-alive on proxies #5168

Job	Run time
Generate llhttp sources	8s
Linter	1m 1s
Test (3.9, ubuntu, false)	6m 23s
Test (3.9, macos, false)	4m 59s
Test (3.9, windows, false)	6m 59s
Test (3.9, Y, ubuntu, false)	6m 10s
Test (3.10, ubuntu, false)	6m 52s
Test (3.10, macos, false)	4m 4s
Test (3.10, windows, false)	6m 5s
Test (3.10, Y, ubuntu, false)	5m 9s
Test (3.11, ubuntu, false)	5m 18s
Test (3.11, macos, false)	4m 1s
Test (3.11, windows, false)	6m 42s
Test (3.11, Y, ubuntu, false)	5m 12s
Test (3.12, ubuntu, false)	6m 47s
Test (3.12, macos, false)	4m 33s
Test (3.12, windows, false)	5m 46s
Test (3.12, Y, ubuntu, false)	5m 45s
Test (pypy-3.9, Y, ubuntu, false)	10m 57s
Test (ubuntu, 3.13, true, Y)	1m 31s
check	3s
Pre-Deploy	0s
Tarball	0s
Build wheels on ${{ matrix.os }} ${{ matrix.qemu }}	0s
Deploy	0s
	1h 44m 25s

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