[CI] Use Download Task for X64 and Bypass ARM Testing for Forked Repositories

[lei9444]

Summary of the Pull Request

Root cause:

Forked repositories cannot obtain an access token for authentication due to the SFI requirement.
ARM experiences an out-of-memory issue when use download task.

PR change:

Skipped the test stage for ARM testing on forked repositories.
Used the download task for X64 to ensure X64 tests always run successfully.

PR Checklist

• Closes: #xxx
• Communication: I've discussed this with core contributors already. If work hasn't been agreed, this work might be rejected
• Tests: Added/updated and all pass
• Localization: All end user facing strings can be localized
• Dev docs: Added/updated
• New binaries: Added on the required places
  • JSON for signing for new binaries
  • WXS for installer for new binaries and localization folder
  • YML for CI pipeline for new test projects
  • YML for signed pipeline
• Documentation updated: If checked, please file a pull request on our docs repo and link it here: #xxx

Detailed Description of the Pull Request / Additional comments

Validation Steps Performed

[lei9444]

/azp run

[azure-pipelines]

Azure Pipelines failed to run 1 pipeline(s).

[yeelam-gordon]

Looks great.

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (2)

.pipelines/v2/templates/pipeline-ci-build.yml:75

• The conditional uses 'platform' while other templates (e.g., job-test-project.yml) reference 'parameters.platform'. Please verify that the correct variable is used for consistency in architecture checks.

-    - ${{ if and(eq(parameters.runTests, true), not(and(eq(platform, 'arm64'), eq(variables['System.PullRequest.IsFork'], true)))) }}:

.pipelines/v2/templates/job-test-project.yml:64

• Confirm that 'parameters.platform' accurately represents the target platform in this conditional and aligns with variables used elsewhere in the CI pipelines to avoid misconfiguration.

+  - ${{ if ne(parameters.platform, 'arm64') }}: