test: Fix --hostuser octal UID test flakiness

[ricardobranco777]

The test for issue #19800 depended on finding a system user with an octal UID. This approach was fragile because system users found on the host may have a different UID in the testing image.

Use the rootless user ID instead which is likely to be octal anyway as new user IDs start with 1000.

Related failure:
https://openqa-assets.opensuse.org/tests/5535030/file/podman-bats-user-local.tap.txt

not ok 88 [030] podman run --hostuser tests # in 1306 ms
# tags: ci:parallel
# (from function `bail-now' in file test/system/helpers.bash, line 187,
#  from function `is' in file test/system/helpers.bash, line 1112,
#  in test file test/system/030-run.bats, line 910)
#   `is "$output" "$octal_userid"' failed
# 
# [09:01:00.631245040] $ /usr/bin/podman run --rm quay.io/libpod/testimage:20241011 grep bernhard /etc/passwd
# [09:01:00.967856561] [ rc=1 (expected) ]
# 
# [09:01:00.973939665] $ /usr/bin/podman run --hostuser=bernhard --rm quay.io/libpod/testimage:20241011 grep bernhard /etc/passwd
# [09:01:01.291043165] bernhard:*:1000:1000:bernhard:/home/podman:/bin/sh
# 
# [09:01:01.301488137] $ /usr/bin/podman run --user=sshd --hostuser=sshd --rm quay.io/libpod/testimage:20241011 id -u
# [09:01:01.651440214] 22
# #/vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
# #|     FAIL: podman run --user=sshd --hostuser=sshd --rm quay.io/libpod/testimage:20241011 id -u
# #| expected: '476'
# #|   actual: '22'
# #\^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
# # [teardown]

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Does this PR introduce a user-facing change?

None

[ricardobranco777]

Verification run:
https://openqa.opensuse.org/tests/5535185/file/podman-bats-user-local.tap.txt

[packit-as-a-service]

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