fix(utils): recognize GitHub-hosted ARM64 Ubuntu and Windows runner labels (#449)

[Tyagiquamar]

Problem

pr_runs_on_self_hosted flags GitHub-hosted ARM64 runner labels (such as ubuntu-24.04-arm, ubuntu-22.04-arm, windows-11-arm, and windows-11-vs2026-arm) as self-hosted runners because the runner matching regex in opa/rego/poutine/utils.rego does not account for -arm suffixes on versioned Linux or Windows 11 runner labels.

Root Cause

job_uses_self_hosted_runner in opa/rego/poutine/utils.rego matched runner strings against ubuntu-(([0-9]{2})\.04|...) and windows-(20[0-9]{2}|...), omitting optional -arm suffixes for Ubuntu labels and Windows 11 ARM variants.

Fix

• Updated job_uses_self_hosted_runner regex in opa/rego/poutine/utils.rego to support ubuntu-NN.NN-arm and windows-11(-vsNNNN)?-arm.
• Added test cases for ubuntu-24.04-arm, ubuntu-22.04-arm, windows-11-arm, and windows-11-vs2026-arm in opa/opa_test.go.

Verification

go test ./opa passed cleanly (100% test suite green).

Fixes #449