This PR fixes a parameter-binding edge case where a scalar PSObject (wrapping a string) was added directly to non-generic IList-backed collection parameters (e.g., StringCollection), causing invalid casts; it now unwraps the scalar value first, matching existing behavior for list elements.

Changes:

• Unwrap scalar values via PSObject.Base(...) before adding them to collection parameters in ParameterBinderBase.EncodeCollection.
• Add a regression Pester test that reproduces the failure shape using a StringCollection parameter and a single pipeline-produced scalar value.

Suppressed comments (1)

src/System.Management.Automation/engine/ParameterBinderBase.cs:1827

• The binding tracer format string uses {1} but only supplies a single argument, so traces will literally print {1} instead of the element type. This makes diagnosing coercion-required cases harder.

                            if (currentValueElementType != desiredElementType &&
                                !currentValueElementType.IsSubclassOf(desiredElementType))
                            {
                                bindingTracer.WriteLine(
                                    "COERCION REQUIRED: Did not coerce scalar arg value to type {1}",

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