[release pipeline] Use of custom gist announcement isn't working

[mthalman]

Setting the announcementGist pipeline parameter for the SB release is intended to use the Markdown contents at that gist URL as the release announcement content. But when setting that parameter, it causes an error when attempting to query the gist in the Submit announcement discussion step: Invalid gist URL <nil>. It's not clear why that is because other log output shows that it has the URL and is correctly defined.

Example failing build (internal link)

[MichaelSimons]

[Triage] As part of fixing this, please ensure the appropriate utests exist to help prevent future regressions with this feature.

[ellahathaway]

We should discuss https://github.com/dotnet/release/issues/1410 first before we begin working on this issue.

[ellahathaway]

Per the discussion in https://github.com/dotnet/release/issues/1410, the automation should be adjusted to pull the custom announcement from a user story.

[ellahathaway]

PR: https://dev.azure.com/dnceng/internal/_git/dotnet-release/pullrequest/54947