fix: Checkout GitHub tools using ref instead of main branch in two more actions

[Mrtenz]

flaky-test-report and update-release-changelog weren't using the new pattern for checking out the proper version of github-tools yet. I've fixed that in this PR.

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Note

Parameterizes and switches both actions to ref-based checkout of github-tools, removing the old version input.

• CI/GitHub Actions:
  • flaky-test-report:
    • Add inputs github-tools-repository and github-tools-ref (default to current action repo/ref).
    • Update checkout to use these inputs and ./github-tools path; rename step.
  • update-release-changelog:
    • Remove github-tools-version input.
    • Add inputs github-tools-repository and github-tools-ref (default to current action repo/ref).
    • Update checkout to use these inputs and ./github-tools path; rename step.

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