ci: linux/arm: reduce parallelism #6118

Job	Run time
Windows 2019/x64	22m 16s
amazon-ecr-auth	3s
macOS 12/x86_64	19m 33s
macOS 12/arm64	10m 45s
Linux dev	11m 58s
Linux amd64	43m 34s
Linux arm64	59m 15s
Linux dev+vendor	1m 8s
Install-check: tgz-ubuntu-22.04/amd64	1m 28s
Install-check: ubuntu-22.04/amd64	31s
Install-check: ubuntu-20.04/amd64	34s
Install-check: ubuntu-18.04/amd64	32s
Install-check: debian-stable/amd64	34s
Install-check: debian-oldstable/amd64	40s
Install-check: amazonlinux-2023/amd64	42s
Install-check: fedora-latest/amd64	38s
Install-check: almalinux-9/amd64	36s
Install-check: almalinux-8/amd64	40s
Install-check: tgz-ubuntu-22.04/arm64	2m 57s
Install-check: ubuntu-22.04/arm64	1m 50s
Install-check: ubuntu-20.04/arm64	1m 27s
Install-check: ubuntu-18.04/arm64	59s
Install-check: debian-stable/arm64	1m 2s
Install-check: debian-oldstable/arm64	51s
Install-check: amazonlinux-2023/arm64	1m 9s
Install-check: fedora-latest/arm64	1m 11s
Install-check: almalinux-9/arm64	1m 2s
Install-check: almalinux-8/arm64	1m 7s
	3h 9m 2s

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