Tests | Address transient errors in CI pipelines

[cheenamalhotra]

All CI pipelines were affected due to these common issues:

• Transient errors when donwloading .NET version
• Mark Flaky tests.
• Fix TestDefaultAppContextSwitchValues to not fail intermittently.

[Copilot]

Pull request overview

Addresses CI flakiness by adding task-level retries to .NET install steps and quarantining two intermittently failing transient-fault failover tests.

Changes:

• Add [Trait("Category", "flaky")] to two retry-disabled transient fault tests in ConnectionFailoverTests.cs.
• Add retryCountOnTaskFailure: 3 to the SDK install, runtime install loop, and ARM64 PowerShell install steps in install-dotnet.yml.

Reviewed changes

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

File	Description
src/Microsoft.Data.SqlClient/tests/UnitTests/SimulatedServerTests/ConnectionFailoverTests.cs	Quarantines two flaky transient-fault retry-disabled tests so they run in the separate flaky pipeline step.
eng/pipelines/steps/install-dotnet.yml	Adds task-level retries to .NET SDK/runtime install tasks to mitigate transient CDN/network failures.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 64.71%. Comparing base (c724554) to head (ad51580).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4314      +/-   ##
==========================================
- Coverage   66.57%   64.71%   -1.86%     
==========================================
  Files         284      279       -5     
  Lines       43301    66219   +22918     
==========================================
+ Hits        28827    42853   +14026     
- Misses      14474    23366    +8892     

Flag	Coverage Δ
CI-SqlClient	?
PR-SqlClient-Project	64.71% <ø> (?)

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