fix: builds no longer fail when symbol upload or release creation is enabled but no Sentry auth token is available

[jamescrosswell]

PrepareSentryCLI runs sentry-cli info to decide whether the CLI is configured, and skips uploads and release creation if it isn't. Since sentry-cli 2.30.0 (#3203), info prints error: Auth token is required… when there's no token, or error: API request failed when the token is bad or the server can't be reached. The probe's Exec ignored the exit code but still parsed that line as an MSBuild error, so the build failed before the skip could happen. That broke every build with SentryUploadSymbols, SentryUploadSources or SentryCreateRelease enabled and no token: fork PRs, local Release builds, and docker build without the secret.

• The probe sets IgnoreStandardErrorWarningFormat="true", so a failing info falls through to the existing skip logic.
• The probe's stderr is logged at normal importance. A successful build no longer prints the CLI's error: … and "Please attach the full debug log" lines at the default verbosity.
• The skip message and warning now say that uploads and release creation are skipped.

Closes #5704

Notes for review

• An invalid or expired token, or an unreachable server, now gives the existing "Sentry API request failed" warning and a successful build, rather than a failed build. That was what the warning was there for, but anyone relying on the failure will notice. -warnaserror still fails the build.
• The release-creation tests now pass the CLI stub to MSBuild through an environment variable rather than /p:SentryCLI. The targets can't clear a global property, so the skip path couldn't be tested the old way. The new cases fail without the fix.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.22%. Comparing base (f5891ee) to head (fb3638b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5705   +/-   ##
=======================================
  Coverage   75.22%   75.22%           
=======================================
  Files         516      516           
  Lines       19022    19022           
  Branches     3698     3698           
=======================================
+ Hits        14309    14310    +1     
+ Misses       3858     3857    -1     
  Partials      855      855           

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