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

[Ankitsinghsisodya]

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]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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

Hi @Ankitsinghsisodya. Thanks for your PR.

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[Copilot]

Pull request overview

Note

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

Fixes an incorrect test failure path in TestTool_Create_Args by reporting the actual tool execution result rather than reusing a stale err value.

Changes:

• Replace t.Fatal(err) with a more informative t.Fatalf(...) when result.IsError is true.

---

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 56.95%. Comparing base (2bbf9fe) to head (076ab1f).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3763      +/-   ##
==========================================
- Coverage   57.06%   56.95%   -0.12%     
==========================================
  Files         181      181              
  Lines       21145    21145              
==========================================
- Hits        12067    12043      -24     
- Misses       7855     7882      +27     
+ Partials     1223     1220       -3     

Flag	Coverage Δ
e2e	35.91% <ø> (ø)
e2e go	31.46% <ø> (ø)
e2e node	27.25% <ø> (ø)
e2e python	31.84% <ø> (+<0.01%)	⬆️
e2e quarkus	27.37% <ø> (ø)
e2e rust	26.75% <ø> (-0.02%)	⬇️
e2e springboot	25.29% <ø> (ø)
e2e typescript	27.35% <ø> (ø)
e2e-config-ci	?
integration	17.35% <ø> (-0.04%)	⬇️
unit macos-14	45.06% <ø> (ø)
unit macos-latest	45.06% <ø> (ø)
unit ubuntu-24.04-arm	45.31% <ø> (ø)
unit ubuntu-latest	46.01% <ø> (ø)
unit windows-latest	45.10% <ø> (ø)

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