ci: fix test-e2e-podman to use matrix.os instead of hardcoded runner

[Ankitsinghsisodya]

Summary

• Fixes test-e2e-podman job which defines a matrix with ubuntu-latest (x86_64) and ubuntu-24.04-arm (ARM64) but had runs-on: ubuntu-latest hardcoded
• Both matrix entries were running on x86_64, so ARM64 was never actually tested on ARM hardware
• Changed to runs-on: ${{ matrix.os }} so each matrix entry runs on the correct runner

Test plan

• Verify the E2E - Podman job spawns two matrix runs: one on ubuntu-latest and one on ubuntu-24.04-arm
• Confirm both matrix entries complete successfully

Fixes #3537

[knative-prow]

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[knative-prow]

Hi @Ankitsinghsisodya. Thanks for your PR.

I'm waiting for a knative member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work.

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[Copilot]

Pull request overview

Fixes the test-e2e-podman GitHub Actions job so its OS matrix actually runs on the intended runner for each entry (x86_64 and ARM64), ensuring ARM coverage is exercised on ARM hardware as intended.

Changes:

• Switch test-e2e-podman from a hardcoded runs-on: ubuntu-latest to runs-on: ${{ matrix.os }}.
• Ensure the matrix’s ubuntu-24.04-arm entry executes on an ARM runner rather than duplicating the x86_64 run.

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[Copilot]

test-e2e-podman uses a matrix but doesn’t set strategy.fail-fast: false. Other matrix jobs in this workflow (e.g., test-unit, test-templates) disable fail-fast so all OS/arch variants still run even if one fails. Consider doing the same here so an early failure on one runner doesn’t cancel the other architecture’s run.