Enable assign-copilot in c9k auto-issue

[sylvainsf]

What

Sets assign-copilot: "true" in .github/workflows/c9k-failure-report.yml.

Why

Follow-up to #11750. We enabled auto-issue (non-dry-run) in that PR but left assign-copilot at "false". Now that we're filing issues for real, also let c9k assign Copilot to the commit/broken-test root-cause issues so they get picked up automatically.

Safety

Per the v2.1.0 action.yml, Copilot is never assigned to flaky-test groups regardless of this flag, those continue to be commented + closed via auto-close-flaky: true.

No other inputs change.

[github-actions]

This PR requires exactly 1 of the following labels: pr:standard, pr:important.
Currently applied labels: .

Label descriptions:

• pr:important - Major features, breaking changes, deprecations, or other high-impact changes that need special attention during release.
• pr:standard - Ongoing maintenance, minor improvements, documentation updates, and routine development work.

@sylvainsf, please add the appropriate label to this PR before merging.

[radius-functional-tests]

Radius functional test overview

🔍 Go to test action run

Click here to see the test run details

Name	Value
Repository	radius-project/radius
Commit ref	2d673ba
Unique ID	func49fe31c1ac
Image tag	pr-func49fe31c1ac

• gotestsum 1.13.0
• KinD: v0.29.0
• Dapr: 1.14.4
• Azure KeyVault CSI driver: 1.4.2
• Azure Workload identity webhook: 1.3.0
• Bicep recipe location ghcr.io/radius-project/dev/test/testrecipes/test-bicep-recipes/<name>:pr-func49fe31c1ac
• Terraform recipe location http://tf-module-server.radius-test-tf-module-server.svc.cluster.local/<name>.zip (in cluster)
• applications-rp test image location: ghcr.io/radius-project/dev/applications-rp:pr-func49fe31c1ac
• dynamic-rp test image location: ghcr.io/radius-project/dev/dynamic-rp:pr-func49fe31c1ac
• controller test image location: ghcr.io/radius-project/dev/controller:pr-func49fe31c1ac
• ucp test image location: ghcr.io/radius-project/dev/ucpd:pr-func49fe31c1ac
• deployment-engine test image location: ghcr.io/radius-project/deployment-engine:latest

Test Status

⌛ Building Radius and pushing container images for functional tests...
✅ Container images build succeeded
⌛ Publishing Bicep Recipes for functional tests...
✅ Recipe publishing succeeded
⌛ Starting corerp-cloud functional tests...
⌛ Starting ucp-cloud functional tests...
✅ ucp-cloud functional tests succeeded
✅ corerp-cloud functional tests succeeded

[Copilot]

Pull request overview

This PR enables Copilot auto-assignment for issues created by the c9k-failure-report workflow, aligning the workflow behavior with the earlier rollout of non-dry-run auto-issue filing.

Changes:

• Set assign-copilot: "true" for the sylvainsf/causinator9000 action invocation in c9k-failure-report.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 51.35%. Comparing base (067781e) to head (2d673ba).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #11752      +/-   ##
==========================================
- Coverage   51.39%   51.35%   -0.04%     
==========================================
  Files         699      699              
  Lines       44111    44111              
==========================================
- Hits        22669    22652      -17     
- Misses      19276    19286      +10     
- Partials     2166     2173       +7     

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