Stop chowning all of ${RUNNER_TEMP} in linux_job/linux_job_v2 - #8598

${RUNNER_TEMP} also holds the runner's own control files --
_github_workflow/event.json, _runner_file_commands/ -- and the recursive
chown we issue from inside an alpine container is not guaranteed to land
on the runner's UID.

On a runner whose docker daemon remaps container UIDs it does not. The
gfx1100 ROCm runners (ctr-navi3x-b13-ws*) run rootless docker (`docker
info` reports DockerRootDir=/home/pytorchci/.local/share/docker), where
container UID 0 maps to the host runner user and container UID N>0 maps
into that user's subuid range. `chown -R $(id -u)` -- the runner's *host*
UID, expanded outside the container -- therefore lands on a subordinate
UID that nothing on the host owns. The runner then cannot read
event.json, and every remaining step of the job fails with

    ##[error]Access to the path
    '/home/pytorchci/actions-runner/_work/_temp/_github_workflow/event.json'
    is denied.

Chown only the three directories we actually hand to the container:
$RUNNER_ARTIFACT_DIR, $RUNNER_DOCS_DIR and $RUNNER_TEST_RESULTS_DIR.
Those are the bind mounts the exec container writes to as root, so they
are the only ones that need restoring, and none of them belong to the
runner. setup-linux, setup-rocm and setup-xpu all set the three env vars
to ${RUNNER_TEMP}/{artifacts,docs,test-results}.

Anything a script writes directly to ${RUNNER_TEMP} as root is no longer
chowned back. linux_job.yml has the same step but is legacy, so it is
left alone.

Hoist the repeated ALPINE_IMAGE expression to a job-level env var rather
than repeat it three times.