redirect output to avoid arch variable contamination

[jrahme-cci]

Description

For the runner manual install some versions of grep caused extra output to enter the arch variable. This PR redirects the /usr/bin/arch stderr and stdout to avoid contaminating the variable with extra output.

Reasons

Issue was raised in an on-prem support workflow https://circleci.slack.com/archives/C05LH7BMR2A/p1713553512725209

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