Create separate flaky tests pipeline

[paulmedynski]

Description

The flaky tests are preventing PR and CI pipeline runs from completing successfully. They don't add any confidence to those pipelines, so we will split them out into their own pipeline. This has many benefits:

• Avoid long-running flaky tests from timing out otherwise successful PR/CI runs.
• Remove the spruious error/warning clutter from the Azure DevOps UIs.
• Consolidate flakiness into its own pipeline we can observe as necessary.

Testing

• The normal PR/CI runs will verify that the regular test runs are still functioning.
• The new Flaky Test CI pipeline will verify the flaky tests.

NOTE: We won't be able to test the new Flaky Tests pipeline until this merges to main. The new YAML file must exist on main before Azure DevOps will allow us to create the new pipeline in the Public project.

[Copilot]

Pull request overview

Splits flaky test execution into a dedicated Azure DevOps pipeline and introduces a flakyTestsOnly switch to run either flaky-only or non-flaky-only test suites via the shared CI templates.

Changes:

• Added a new CI-SqlClient-Flaky pipeline YAML that runs only flaky tests on main (CI + weekday schedule).
• Plumbed a new flakyTestsOnly boolean parameter through dotnet-sqlclient-ci-core.yml → ci-run-tests-stage.yml → ci-run-tests-job.yml → run-all-tests-step.yml.
• Refactored the test-running step template to conditionally run flaky vs non-flaky test targets (and mark flaky runs continueOnError).

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
eng/pipelines/sqlclient/sqlclient-flaky-tests-pipeline.yml	New pipeline definition that extends the core template with flakyTestsOnly: true.
eng/pipelines/dotnet-sqlclient-ci-core.yml	Adds flakyTestsOnly parameter and forwards it into the test stage template.
eng/pipelines/common/templates/steps/run-all-tests-step.yml	Adds conditional branching to run flaky-only vs non-flaky-only test tasks.
eng/pipelines/common/templates/stages/ci-run-tests-stage.yml	Accepts/forwards flakyTestsOnly into test jobs.
eng/pipelines/common/templates/jobs/ci-run-tests-job.yml	Accepts/forwards flakyTestsOnly into the test execution step template.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 67.55%. Comparing base (a0357b2) to head (7ca6b0c).

❗ There is a different number of reports uploaded between BASE (a0357b2) and HEAD (7ca6b0c). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (a0357b2)	HEAD (7ca6b0c)
addons	1	0

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #3936       +/-   ##
===========================================
- Coverage   90.82%   67.55%   -23.28%     
===========================================
  Files           6      263      +257     
  Lines         316    66198    +65882     
===========================================
+ Hits          287    44718    +44431     
- Misses         29    21480    +21451     

Flag	Coverage Δ
addons	?
netcore	67.63% <ø> (?)
netfx	66.45% <ø> (?)

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