.NET Workflows - Add unit tests for ConditionGroupExecutor

[Copilot]

Motivation and Context

Unit test coverage for ConditionGroupExecutor was missing.

Description

Adds ConditionGroupExecutorTest with 100% line coverage of ConditionGroupExecutor.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR.

[Copilot]

Pull request overview

Adds missing unit test coverage for ConditionGroupExecutor in the declarative workflows object model, and refactors existing tests to reuse a shared IsDiscreteAction assertion helper.

Changes:

• Add ConditionGroupExecutorTest covering condition evaluation, branching, and step naming.
• Refactor WorkflowActionExecutorTest/ForeachExecutorTest to centralize IsDiscreteAction verification.
• Modify ConditionGroupExecutor.Steps.Else behavior (removes the prior fallback name).

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 6 comments.

File	Description
dotnet/tests/Microsoft.Agents.AI.Workflows.Declarative.UnitTests/ObjectModel/WorkflowActionExecutorTest.cs	Adjusts test execution helpers and adds a shared VerifyIsDiscrete assertion.
dotnet/tests/Microsoft.Agents.AI.Workflows.Declarative.UnitTests/ObjectModel/ForeachExecutorTest.cs	Switches inline reflection assertion to the shared VerifyIsDiscrete helper.
dotnet/tests/Microsoft.Agents.AI.Workflows.Declarative.UnitTests/ObjectModel/ConditionGroupExecutorTest.cs	New unit tests for ConditionGroupExecutor behavior and naming conventions.
dotnet/src/Microsoft.Agents.AI.Workflows.Declarative/ObjectModel/ConditionGroupExecutor.cs	Changes else-step naming behavior by removing the default fallback.