fix(mcp): use result in error message instead of nil err in create test

[Ankitsinghsisodya]

Note: Re-submission of #3763, accidentally closed when the head repository was deleted.

Problem

In TestTool_Create_Args, after a successful client.CallTool call, the error branch reads:

if result.IsError {
    t.Fatal(err) // err is nil here
}

CallTool returned (result, nil) — err is guaranteed nil at this point since it was already checked on the lines above. If result.IsError ever triggers, t.Fatal(nil) prints <nil>, giving zero diagnostic information about what actually failed.

Fix

Replace with the pattern used consistently across every other tool test in this package:

if result.IsError {
    t.Fatalf("unexpected error result: %v", result)
}

No behaviour change — this only affects the failure message when the test fails.

[knative-prow]

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This pull-request has been approved by: Ankitsinghsisodya
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[knative-prow]

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[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Fixes an incorrect fatal assertion in TestTool_Create_Args so the test reports the actual tool result when the tool execution returns an error.

Changes:

• Replace t.Fatal(err) (which may be nil/stale) with a descriptive failure message that includes result.

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