Fix InstallAspireCliFromPullRequest to use WaitForSuccessPromptFailFast

[Copilot]

InstallAspireCliFromPullRequest was missed in the original fix (#14934) — it still used WaitForSuccessPrompt despite downloading from the GitHub API via curl, making it susceptible to the same HTTP 502 failures described in issue #14933.

Description

Changed WaitForSuccessPrompt → WaitForSuccessPromptFailFast in InstallAspireCliFromPullRequest to match the behavior of InstallAspireCliRelease and InstallAspireCliDaily.

// Before
.WaitForSuccessPrompt(counter, TimeSpan.FromSeconds(300));

// After
.WaitForSuccessPromptFailFast(counter, TimeSpan.FromSeconds(300));

Checklist

• Is this feature complete?
  • Yes. Ready to ship.
  • No. Follow-up changes expected.
• Are you including unit tests for the changes and scenario tests if relevant?
  • Yes
  • No
• Did you add public API?
  • Yes
  • No
• Does the change make any security assumptions or guarantees?
  • Yes
  • No
• Does the change require an update in our Aspire docs?
  • Yes
  • No

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