fix: ensure BodyPartReader.read() returns bytes, not bytearray #16600

Job	Run time
Linter	1m 13s
Generate llhttp sources	11s
Pre-Setup global build settings	2s
Benchmark	11m 33s
Cython coverage (windows)	2m 48s
Cython coverage (ubuntu)	2m 5s
Autobahn testsuite (3.14, ubuntu)	11m 38s
Test (3.10, ubuntu, false)	4m 52s
Test (3.10, windows, false)	5m 48s
Test (3.12, ubuntu, false)	4m 24s
Test (3.10, macos, false)	9m 43s
Test (3.12, windows, false)	6m 16s
Test (3.12, Y, ubuntu, false)	5m 57s
Test (3.10, Y, ubuntu, false)	6m 13s
Test (3.12, macos, false)	6m 39s
Test (3.14, windows, false)	6m 27s
Test (3.11, windows, false)	5m 56s
Test (3.11, Y, ubuntu, false)	5m 55s
Test (3.14, macos, false)	7m 6s
Test (3.14, Y, ubuntu, false)	7m 51s
Test (3.13, Y, ubuntu, false)	5m 14s
Test (pypy-3.11, Y, ubuntu, false)	9m 40s
Test (3.11, ubuntu, false)	5m 1s
Test (3.13, macos, false)	6m 32s
Test (3.13, windows, false)	6m 19s
Test (3.13, ubuntu, false)	4m 27s
Test (3.14, ubuntu, false)	4m 40s
Test (ubuntu, 3.14t, false)	3m 55s
Test (3.11, macos, false)	6m 56s
check	6s
Pre-Deploy	-1s
Build wheels on ${{ matrix.os }} ${{ matrix.qemu }} ${{ matrix.musl }}	0s
Tarball	0s
Deploy	0s
	2h 45m 26s

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