Don't truncate the last character in ttyname #3227

Job	Run time
Check selected Tier 3 platforms (nightly)	6m 13s
Check --no-default-features (nightly)	1m 11s
Check (stable)	8m 39s
Check nightly-only targets (nightly)	31s
Check (nightly)	8m 3s
Rustfmt	9s
Check (1.63)	14m 26s
Test rustix_use_experimental_asm (powerpc64le-linux)	1m 30s
Test (ubuntu)	1m 15s
Test (ubuntu-20.04)	1m 23s
Test use-libc (ubuntu)	1m 7s
Test (i686-linux)	1m 35s
Test use-libc (i686-linux)	1m 35s
Test (aarch64-linux)	1m 34s
Test use-libc (aarch64-linux)	1m 38s
Test (powerpc64le-linux)	1m 35s
Test use-libc (powerpc64le-linux)	1m 41s
Test (riscv64-linux)	1m 26s
Test use-libc (riscv64-linux)	1m 41s
Test (s390x-linux)	1m 32s
Test use-libc (arm-linux)	1m 28s
Test (arm-linux)	1m 35s
Test (ubuntu-stable)	1m 29s
Test (ubuntu-1.63)	3m 55s
Test (i686-linux-stable)	1m 42s
Test (aarch64-linux-stable)	1m 48s
Test (riscv64-linux-stable)	1m 52s
Test (s390x-linux-stable)	1m 26s
Test (powerpc64le-linux-stable)	1m 45s
Test (arm-linux-stable)	1m 58s
Test (ubuntu-1.63)	3m 57s
Test (i686-linux-1.63)	4m 19s
Test (aarch64-linux-1.63)	4m 33s
Test (riscv64-linux-1.63)	4m 35s
Test (s390x-linux-1.63)	4m 24s
Test (powerpc64le-linux-1.63)	4m 58s
Test (arm-linux-1.63)	4m 53s
Test (macos-latest)	2m 40s
Test (macos-11)	1m 16s
Test (windows)	1m 9s
Test (windows-2019)	1m 24s
	1h 55m 50s

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